CHAPEL HILL, N.C. -- This was supposed to be like every other Clemson game this season, a blowout win piled onto another blowout win on its easy road back to the College Football Playoff.

After all, the No. 1 Tigers went into their matchup against unranked North Carolina as 28-point favorites, and as the team with the highest probability to make it into the playoff at a whopping 76.6%. No ranked teams left on the schedule in the weak ACC? No problem.

Except teams do not always fit into neat, tidy, easy-to-predict boxes.

So it was that Clemson faced its fiercest challenge to date, as North Carolina outplayed and outcoached the top-ranked team in the country for most of the day.

But just the way the Tigers did in close games last season, they came up with the crucial play with the game on the line -- this time, stopping North Carolina's 2-point conversion attempt with 1:17 remaining to win 21-20 on Saturday.

"It's not easy to win," Clemson coach Dabo Swinney said. "I know we're supposed to destroy everybody, like nobody else has scholarships, nobody else has coaches. It doesn't work that way. We're just normal people. There's nothing special about us. We're not perfect. We don't coach perfect. Unfortunately, we don't play perfect every down, every game, but we found a way to win an ugly game.

"But it's disrespectful to just put it all on us. You've got to give them some credit. Those kids played their heart out, and they coached their hearts out, and they played with tremendous will to win, but I'm proud of my guys because they found a way when we had to have it. We found a way."

The two teams were deadlocked at 14 until Trevor Lawrence threw a perfectly placed ball to Tee Higgins for a 38-yard touchdown to give Clemson (5-0, 3-0 ACC) its first lead of the game, 21-14 with 9:54 to play. But North Carolina and freshman quarterback Sam Howell marched right down the field on a 16-play drive, converting twice on third down and twice on fourth down to stay in the game.

On first-and-goal from the 3, Howell threw a 2-yard pass to Jake Bargas to put North Carolina at the 1-yard line with 1:19 left. At this point, Swinney had a feeling North Carolina coach Mack Brown would go for 2 and the win if his team successfully punched it in. Sure enough, the Tar Heels (2-3, 1-1) scored on the next play and Brown signaled for 2.

"I've always had the theory that the longer the game goes, the best team wins, and they have the best team," Brown said. "So my thought was, 'Go now.' We've got momentum, they're tired, they're on the field, so that was the best chance for us to win the game."

Brown said he asked offensive coordinator Phil Longo, "Do you have a play that you think is going to work to score to win the game, to beat the No. 1 team in the country?"

"And he said, 'Yes.'"

The call was an option for Howell, and it was a similar play to a 2-point conversion North Carolina converted earlier in the season. Clemson linebacker James Skalski said, "I think we had a good idea they were going to go with an option look, and it showed up. We were ready for it."

Howell ran to his right, and saw his receiver option covered up. He kept running, but Clemson was on him, as Skalski, Xavier Thomas and Nolan Turner converged. Howell tried to pitch, but it was too late.

"It did not unfold how we wanted to, obviously," Brown said. "Sam fought his guts to get in. You work on 2-point plays all the time and Phil was very confident. If he had said he wasn't sure, we kick."

Added Skalski: "North Carolina played their butt off. They had a good plan. They made plays, but when it mattered most, we showed up."

Going into the game, Clemson had beaten each of its past 14 opponents by double digits, helping feed into the narrative that the Tigers wouldn't face another test this season -- particularly with zero ranked teams left on the schedule.

But they were in two close contests in the first half of last season. They had to stop a 2-point conversion attempt that would have tied the score against Texas A&M. Then against Syracuse, nearly one year ago, the Tigers needed a fourth-quarter comeback to win.

"There's been a game every year the past four years or so in this program where it's been close or we lost," Lawrence said. "We know it's hard to win. Sometimes it's easy to forget that when you win so many games by so many points, but this game is only going to make us better. Obviously, we'd like to win every game by four touchdowns, but it's going to bring us closer and show us how to appreciate every win and like tonight, just finding a way."

Clemson had its worst offensive performance of the season, with lows in total points, total yards and passing yards. A big reason why is because the Tigers made crucial mistakes the entire game, from procedure penalties, to a fumble, to a missed field goal attempt, to lapses on third down.

North Carolina dared Clemson to run, taking away its talented receivers and forcing Lawrence to do more on the ground than anyone anticipated going into the season. Clemson has an off week before hosting Florida State on Oct. 12, and Swinney said he was going to relish film study on Monday when it points out all the errors his team made.

"Whether you win by one point or 50 points, it's a win," Swinney said. "It's kind of like when I make a birdie in golf. Most times when I make a birdie it usually hits off a tree, runs across the green, hits off the golf cart, bounces back up there close to the flag, and I putt it in and I write 3 on the scorecard. There ain't no pictures on the scorecard. A win is a win, and I'd rather learn lessons with a win than learn with a loss any day."