Without Mack in the lineup for the first time in his six-year career, the Browns hardly got anything going on the ground in a 24-6 loss at Jacksonville.
Cleveland ran 30 times for a season-low 69 yards, and without the help of play-action passes, Brian Hoyer was hurried and harassed into several poor throws and a couple of mistakes.
"We got our butts kicked," Hoyer said. "They handed it to us."
And with not much of a running game, Hoyer found himself in trouble most of the day. He completed 16 of 41 passes for 215 yards, with an interception. He also was sacked three times and fumbled.
"This is disappointing," Browns left tackle Joe Thomas said. "That's the nature of this league. You win one game and you're crowned Super Bowl champions. You lose a game and you're announced as the worst team in the league. I hope we have the perspective to know that's the way it goes in the NFL."
The Browns (3-3) settled for field goals in two trips inside the 20-yard line and failed to convert on fourth-and-1 at the 24. Cleveland managed just three points off rookie Blake Bortles' three interceptions.
"When you get turnovers, you've got to turn them into points not field goals," Browns coach Mike Pettine said. "When you're only kicking field goals, you start to press."
No doubt, though, Cleveland's biggest problem was stagnant ground game. The Browns entered Sunday with the league's third-best rushing attack, but it held in check most of the day.
Playing without Mack may have been the culprit.
The Browns made two changes along their offensive line in an effort to replace Mack, who broke his left leg last week and had season-ending surgery. Right guard John Greco slid to center, and Paul McQuistan, who was with Seattle last season, stepped in at guard.
The Jaguars took advantage, getting steady pressure up the middle.
"When you don't have the best center in the NFL, you have someone that's less than the best," Thomas said. "But if we had played to our standard, I think we would have been OK."
Hoyer didn't want to use Mack's absence as an excuse. He credited Jacksonville's defense for posing problems at every position. But Jaguars defensive tackles Sen'Derrick Marks and Roy Miller gave Cleveland fits inside.
"Remember, that's a good front seven we faced," Hoyer said. "That could probably be the best front seven on defense that we've played. You can't replace Alex Mack, but that's no excuse for us. We showed that last week that we can replace him, but today we just got outplayed."
Hoyer's mistakes were costly, too. He lost a fumble that led to a field goal in the third quarter and threw an interception in the fourth.
The fumble was questionable, but it was upheld after officials reviewed the replay.
"I threw it as I was getting hit," Hoyer said. "When I let it go, I didn't even try to get up and get the ball because I thought it clearly was an incompletion."
His play could rekindle debate about how long first-round draft pick Johnny Manziel will stay on the sideline. Hoyer had been solid all season, but that was with a dynamic running game.
Now, the question remains whether the Browns can get it back without Mack in the mix. Or whether Hoyer can step up his play without the same kind of ground game.
"We weren't running the ball well and we were in second-and-9, third-and-10, and that's tough on any quarterback," Pettine said. "We knew it would be a big challenge for us. That was good defensive line play by them to get their hands up and knock down some passes. That's frustrating when you have guys open down the field and you can't get the ball to them."