Williams, who in his previous three games scored just 20 points combined, finished with 23 points, including a career-high 13 free throws; all the while giving UNC (15-7, 5-6 ACC) a physical presence it has missed since Williams suffered a series of injuries dating back to December.
"What doesn't kill you makes you stronger," Williams said. "I went out there with a mentality that I was going to have to deliver a hit or get hit."
League scoring leader Rashad McCants scored a game-high 25 points, a total he has equaled or eclipsed in seven of his last nine games.
Sean May and Jackie Manuel each scored 14 points and Melvin Scott added 13. It was May's tenth double-double this season and his third in the last four games.
However for the first time in his collegiate career, Raymond Felton failed to score a field goal, going 0-for-4 from the floor. Felton managed 16 points in the first meeting, but John Gilchrist's defense did force him into a less than impressive 5-for-11 shooting night.
"That was an interesting match-up because Felton is so quick and John is so strong," Maryland coach Gary Williams said. "We didn't do anything special except try to stay in front of him. He's so quick going sideways and he can change direction so well."
McCants is enjoying his best stretch of play since he burst on the scene as a freshman.
"Most people say he's hot or he's just feeling it, blah, blah, blah," McCants said. "But I feel like I should have been playing like this since the beginning of the year, when I wasn't aggressive enough and struggled a little bit with my shot."
He was certainly feeling it when he scored 12 first half points on 5-of-7 shooting, pulled down five rebounds and blocked two shots before intermission. He seemed to be having the most fun playing as he ever has.
But when he misfired on a full wind-up windmill dunk attempt with no defender in sight, Roy Williams became so furious he wouldn't even look at McCants after he was fouled attempting a put back of the miss. Williams just stared off in the other direction, with steam hissing from out of his collar.
Yet in actuality, Williams was already hopping mad during the previous timeout, after the Terps had executed a 13-6 run to start the second half and cut a 20-point lead down to a workable margin.
Williams had seen this too many times before, like for instance in the teams' previous meeting at College Park, when Carolina blew an early 10-point lead eventually losing 90-84 after having just knocked off then top-ranked Connecticut.
"Do you want to know why coaches don't carry guns, just watch our team," Roy Williams said. "This season has been so up and down. The inconsistency that we're playing with is mind boggling."
By halftime, the Tar Heels had blistered the nets for 55 points at a 58.1-percent shooting clip, with four players in double figures, a 30-16 rebounding edge, and both Travis Garrison and Chris McCray had three fouls apiece.
But with the same severity with which the Tar Heels can score points in bunches, they can "drought" with the best of them, too.
With 11:28 still remaining in the game, Maryland had cut its deficit to nine points, largely due to the Terps' pressing and getting easy baskets from it.
Roy Williams: "When you're up by 20 points and you've just shot 58.1-percent and held your opponent to 30-percent, when Coach says in the locker room, ‘C'mon guys you've got to do better,' they don't listen to you."
What looked like a blowout just minutes prior was falling closer and closer within range of a potential disaster. After all, Carolina really had to have this game regardless of being ranked all season long, to avoid falling even deeper into the depths of the ACC standings.
A three-pointer by Jamar Smith would make it 72-66 with just over ten minutes left. Meanwhile, McCants' missed dunk may have been in his head, as he missed two wide-open three-point attempts in a row.
"We have 20-point leads and then we break down so badly," McCants said. "It's so unfortunate."
A three by Gilchrist with 4:52 to play made it 82-79, but McCants nailed a three and then Melvin Scott scored on a layup to quickly push the Tar Heels' lead back to eight. After Maryland pulled back to within four, McCants banked in a miraculous three with the shot clock running down, and then May scored on a fast break dunk as Carolina had finally salted away victory.
"The glass was kind," Gary Williams said of McCants' buzzer-beater. "I told my players not to take any satisfaction in coming back and not getting the win. I thought we had a chance to win the game, but we took some bad shots and we paid the price."
The Terps (13-8, 4-6 ACC) play four of their next six games at home.
The Tar Heels don't play again until next Saturday when they host Florida State. Roy Williams will give his players two days off this week.
"I've never practiced a team as easy as I've have this one…and I want to make sure we have legs," Roy Williams said. "But bad legs don't make you make bad decisions."