ATLANTA — When Clemson and Notre Dame met in their 2015 epic battle in Death Valley, Clemson went up 21-3 early in the third quarter and seemed as if it had the game in hand.

However, the Irish fought back behind the play of quarterback Deshone Kizer and came within a two-point conversion in the last seven seconds of forcing overtime as the Tigers hung on for a 24-22 victory.

Though No. 2 Clemson went on to play for the national championship that season, racing out to big leads and then allowing its opponent to come back became a theme that season for the Tigers. They did it seven times that year.

Lack of depth on defense played a big role in why the Tigers struggled to close out games in 2015.

When Notre Dame head coach Brian Kelly looks at this year’s Tigers, the one thing he has noticed is that they finish off their opponents.

Clemson, who will play the third-ranked Irish in the Cotton Bowl on Dec. 29 as part of the College Football Playoff, has won eight straight games by 20 or points this season, while 11 of its 13 wins have been by 20 or more points.

“Obviously, when you talk about playing an opponent, it’s the ability to close games out, the ability to know how to win, and that’s Clemson,” Kelly said during the CFP’s Coaches Press Conference at the College Football Hall of Fame in Atlanta on Thursday. “They know how to win football games. They’ve been winning.

“I think everybody that’s up here has developed and built a winning culture within their football team. You can’t pin that on any one particular player. That’s something that’s within the fabric of the football program that’s been built over time. So that would be the X factor.”

Clemson’s Dabo Swinney could not pin the Irish’s success on one player, either. However, the Tigers’ head coach knows Clemson’s going to play a team that has been battled tested all season and knows how to win any kind of football game.

“They’ve been in some great venues this year, some unique places that they’ve had to go play,” he said. “They’ve played some excellent teams, and they have — they’ve had a lot of different challenges. I’m just kind of really diving in deeply into their season. But they’ve handled adversity. They’ve played with leads. They’ve come from behind. They’ve done a little bit of everything.”

Notre Dame’s X Factor is it is a confident football team that believes in everything it does, which is why it is 12-0 and is making its first appearance in the CFP.

“They’re incredibly well coached. They don’t make a lot of mistakes, and I think the balance that they have really presents some problems,” Swinney said. “This quarterback (Ian Book) and the change we went through, kind of a similar thing that they did, and their quarterback has just grown and grown and grown as the season has gone.

“I would just say the confidence and the fact that they’re battle tested and from the experience that they’ve had this year gives them every reason to be confident going into this postseason.”