Brady leads the NFL's highest-scoring offense. NFL sacks leader Aldon Smith spearheads a 49ers defense that has allowed the fewest points.
The Patriots have gained the most yards in the league and are in the top seven through the air and on the ground. The 49ers have allowed the second-fewest yards overall with a balanced defense: second against the pass and tied for second against the run.
So when two of the top Super Bowl contenders meet, with both hoping to move closer to a first-round bye and home-field advantage throughout their conference playoffs, it will be strength against strength.
The Patriots (10-3) have clinched the AFC East and are tied with Denver for the second-best record in the conference, but hold the tiebreaker because they beat the Broncos. The 49ers (9-3-1) have the second-best mark in the NFC and can lock up first place in the West by beating the Patriots if Seattle loses to Buffalo. Even if the Seahawks win, the 49ers clinch a playoff spot if they beat the Patriots.
That won't be easy.
Brady has made lots of superior defenses look soft.
Just last Monday night, he threw touchdown passes on his first three series and another in the third quarter in a 42-14 rout of Houston. Having the NFL's best record at the time and the AFC's leading sacker, J.J. Watt, didn't help the Texans once Brady went to work.
The 49ers have Smith, whose 19½ sacks are just three shy of the single-season record set by Michael Strahan with the New York Giants in 2001.
"There's no real weakness on this defense and they do everything well," Brady said. "You have to do everything well, too."
He usually does, especially in December. The Patriots have won their last 20 games at home in that month.
Niners counter with versatile Kaepernick at QB
The 49ers, meanwhile, have a quarterback making just his fifth NFL start. The mobile Colin Kaepernick had strong performances in his first two starts, but the offense struggled in the past two games despite having the league's second-ranked rushing attack. His inexperience could hurt against an improving defense.
"He hasn't played in many games, but he's been very productive," Patriots safety Devin McCourty said.
It's on defense where the 49ers excel.
They've allowed just 14.2 points per game and haven't given up more than 26. The Patriots are averaging 19.5 in the first half alone and have scored more than 26 in 10 games.
And New England has Wes Welker, who needs five catches to become the first receiver with at least 100 in five seasons.
"We all have to go out there and win out one-on-one battles," cornerback Tarell Brown said. "They have a lot of different weapons, a lot of guys that can make plays, but we're really fighting against Tom Brady. He has the keys to the car and we definitely have to stop him."
The 49ers must guard against being fooled. Brady is outstanding on play-action passes like the 37-yard touchdown he threw to a wide-open Brandon Lloyd against the Texans. With Stevan Ridley in the midst of a 1,000-yard rushing season, New England's running game is dangerous, too.
"Tom Brady's mechanics are really good and they do a good job disguising things," Smith said, "so you have to not only be disciplined but try to anticipate and pay attention to the film so, come game time, we're not caught off-guard by anything."
The two-time MVP quarterback is having another brilliant season with 29 touchdown passes and four interceptions. He's been remarkably consistent, completing at least 60 percent of his passes in every game, and been sacked only 20 times.
Sack artist Smith looking to bring down Brady
But here comes Smith.
"I face a bunch of good pass rushers," Patriots left tackle Nate Solder said. "It seems like every week it's a top pass rusher. So I guess that's the excitement of playing in the NFL."
Smith was drafted with the seventh pick in 2011, just four spots before Watt, and both have made powerful impacts. But Monday night, Watt was held without a sack for only the third time this season after getting six in his previous three games.
What worked against the Texans, though, may not work against the 49ers. Smith has at least one sack in seven consecutive games and 14 over San Francisco's past six games.
"They're different schemes and different players," Brady said. "I think they both rush the passer well. I think they're both good in coverage. That's why you win a lot of games, because you're really fundamentally sound in all of those areas. But in terms of style, they are very different teams. But it's equally as big of a challenge for us."
For the 49ers, too. They can't focus too much on the passing game, not with Ridley leading the NFL's seventh best running game with 1,082 yards.
So too much pressure on the quarterback can be a bad thing.
"Any team that just goes out there and blitzes away is going to get blown out," San Francisco safety Donte Whitner said. "You can't do that. You have to mix it up. Any quarterback that's this good – that's an A-plus at the helm – you have to mix some things. Everybody knows that you can't go out there and do one thing. You have to do multiple things. With our personnel and our scheme, I believe that allows us to do it."
There's no better test of that than the Patriots.
Niners QB will provide his own test for Pats
Kaepernick is giving New England some extra things to think about this week.
As if defending perennial Pro Bowl running back Frank Gore wasn't enough of a concern, the Patriots now must focus on curtailing San Francisco's shifty quarterback in front of a national audience.
''Our job is to contain him, running and passing,'' New England defensive end Chandler Jones said. ''Kaepernick's a good athlete. He can throw the ball and he can run as well. It's our job to contain him.''
Easier said than done.
The Miami Dolphins last week discovered first-hand how difficult that task can be.
Trailing by seven late in the fourth quarter, the Dolphins' defense surrendered a 50-yard touchdown run to Kaepernick, who deftly deceived the defensive line with a perfect play-action fake, bounced outside and darted untouched up the left sideline for the clinching score for the 49ers.
''Everybody came to me and Mr. Everything did his thing,'' Gore said after the win.
The highlight-reel run also served noticed to the rest of the league – there is no quarterback controversy in the Bay Area.
''He's a guy that can do a lot. Just that last run he had against Miami last week where he's able to just hit the sideline and pull away from everybody and he has a very strong arm,'' Patriots safety Devin McCourty said. ''So, another young quarterback that we're playing that we're going to just try to make things tough on him, do different things, but he's really grasped onto the offense fast."
Kaepernick's primary numbers don't jump out at you – three passing touchdowns, five touchdown runs and a 67.4 completion percentage. Yet the 25-year-old has just one interception in 129 pass attempts, has eclipsed 200 yards passing in three of his four starts and is averaging 7.6 yards per carry.
''He has one interception. As a young guy to be playing football and playing at a high level like he's doing, he's not making many mistakes at all and he's not throwing into coverage where guys are just dropping balls,'' McCourty said. ''I think because of his arm strength, he's able to even throw in some tight windows and get the throw in there and it's the right read. So it's going to be tough for us.''
Kap's impact goes beyond the numbers
San Francisco coach Jim Harbaugh earlier this week highlighted Kaepernick's top qualities, saying he's fast, powerful, smart and reads the field extremely well.
Patriots coach Bill Belichick sees similar talents.
''I think the two most important things for a quarterback are his decision making and accuracy. I could probably go out there and read the field decently but I don't think you'd want me playing quarterback,'' Belichick joked. ''There are other guys that can thread a needle but maybe not see as well, but I think the combination of seeing the field, making good decisions and accuracy is really what it comes down to more than some other qualities.
''I think he's done it to a degree,'' he added. ''He's a young, improving quarterback. It looks like he gets better each week and probably plays with more confidence and does things a little bit better each week. But, I wouldn't disagree with (Harbaugh).''
Kaepernick started the season as the backup to Alex Smith, who just last season led San Francisco to within one victory of the Super Bowl and had the 49ers at 6-2 and atop the NFC West before going down with a concussion in the first half against St. Louis on Nov. 11.
The 36th overall pick in the 2011 draft then calmly stepped under center and inherited the starting role even with Smith healthy enough to return.
''This guy, he can throw the football, he has a strong arm, he's pretty accurate. For the most part, he makes pretty good decisions,'' said New England nose tackle Vince Wilfork. ''To be playing only a couple of weeks, he makes some good plays for this team.''
The Patriots defense, however, poses perhaps the most formidable test yet for the mobile quarterback.
Their run defense is eighth in the league, surrendering just more than 100 yards a game. And while the unit still ranks 29th against the pass, it has vastly improved since the acquisition of cornerback Aqib Talib, who has played in four games for the AFC East champions. New England has won seven straight, including a dominating 42-14 victory over the first-place Houston Texans on Monday.
''Defensively, turnovers and points allowed, that's really what decides the game,'' McCourty said. ''We can pull up a bunch of different stats, but how many points have you given up and try to take the ball away. So for us, it stays the same throughout the season.
''We'll have our work cut out for us this week. This team and this offense, they do a good job of taking care of the ball, so we're really going to have to try to go out there and make our own plays in the passing game and running game.''
For the 49ers to win, so will Kaepernick.
Can Kap pull off a Brady in second season?
In his second season, Brady led New England to a Super Bowl victory after taking over as the starting quarterback during the year.
Kaepernick is hoping to pull off the same feat with the 49ers.
Brady's Patriots will be looking for their 14th straight win in December and 21st straight at home during the month. They've already clinched the AFC East title and trail Houston by one game for the conference's top seed.
The first-place Niners are slightly behind the Patriots as far as having their division wrapped up, but San Francisco can win the NFC West on Sunday with a win and a Seattle loss to Buffalo.
"It's a great opportunity to go out and show what we're capable of," Kaepernick said. "They're going to give you a lot of different looks on defense. You just have to be ready for it."
While New England went 11-3 in 2001 after Brady replaced the injured Drew Bledsoe in Week 2, the 49ers have won three of Kaepernick's four starts since Alex Smith suffered a concussion against St. Louis on Nov. 11.
Kaepernick was 18 of 23 for 185 yards in a 27-13 win over Miami on Sunday. He's completed 67.4 percent of his passes as a starter and averaged 8.3 yards per attempt.
Kaepernick showed off his running ability with a late 50-yard touchdown to seal the victory over the Dolphins. He's already third among NFL quarterbacks with 351 yards on the ground – 7.6 per carry – and five rushing touchdowns.
"There are definitely things that we're doing that tailor the offense to his skill set,'' coach Jim Harbaugh said.
The Patriots have done plenty to tailor their prolific offense around Brady, who has 19 touchdown passes and just one pick during the team's seven-game winning streak.
"It needs to come together now,'' Brady said. "This is the perfect time for it. We can't wait any longer.''
Brady's receiver corps a bit banged up
Brady will try to make the most of a banged-up receiving corps after Donte' Stallworth (ankle) and Julian Edelman (foot) were placed on injured reserve this week.
As a result, the team re-signed Deion Branch for the second time this season.
With tight end Rob Gronkowski also out with a broken forearm – he's listed as questionable on New England's injury report after returning to practice in limited fashion Friday – Aaron Hernandez stepped up nicely with eight catches for 58 yards and two scores against Houston.
Ridley will try to continue to give the Patriots a solid option in the running game after scoring a touchdown in six consecutive contests.
The 49ers, though, have given up just three rushing scores – tied for the league lead. They're also tied for second in rushing defense at 90.8 yards per game.
"We're going to be able to see where we are as a defense,'' Whitner said. "We understand who's going to have to win that football game, and we think it's going to be the defense."
The Patriots' defense has improved the past two weeks, allowing an average of 300.0 yards after yielding 390.2 yards per game through their first 11 contests.
The 49ers would love to get star tight end Vernon Davis more involved after he's totaled three catches for 19 yards in the last three games.
San Francisco, though, doesn't figure to shy away from its versatile running game. Behind Gore, the 49ers rank second in the league at 161.5 yards per game.
They'll want to wear down the Patriots, who rank eighth against the run (100.8) after holding Houston's Arian Foster to 46 yards and a touchdown on 15 carries.
"We know we're a good defense here," Patriots cornerback Devin McCourty said. "We know we've played really well the last couple of weeks and the biggest focus for us is just trying to build on that.''
New England looks for its fourth straight victory over the 49ers, winning the last meeting 30-21 with Matt Cassel under center on Oct. 5, 2008, at Candlestick Park in San Francisco.