Call it the biggest game of the year for Duke.

It could have been a third straight romp for No. 15 North Carolina, which averages more than 450 yards per game.

In fact, it looked like it would be just that. The Tar Heels scored three touchdowns and racked up 251 yards on their first four drives.

But then the Blue Devil defense buckled down, finally coming up with key stops in the game’s pivotal moments.

When North Carolina drove to open the third quarter, the game was tied at 21. And in of the the contest’s turning points, senior safety Deondre Singleton made one of Duke’s most spectacular plays of the season.

With a Tar Heel wideout breaking free across the middle, Singleton jumped into the passing line, deflecting the pass near the line of scrimmage before turning around to haul it in at the Blue Devils’ 27-yard line.

“He sure was pumped up. If it had been NFL rules, he would have scored because he got up and took off with the ball,” Duke head coach David Cutcliffe said. “The biggest key for us defensively in the second half was making them have to snap the ball multiple times every drive…. If we just make them snap it enough times, we will create something.”

The third interception of the season for junior quarterback Mitch Trubisky—and first in weather conditions that did not involve a hurricane—led the defense to crack down even more on a player who started the game completing 12-of-15 passes for 200 yards and all three North Carolina touchdowns.

No defender elevated his game from the first half to the second more than freshman Mark Gilbert, who started the game at cornerback after senior Breon Borders suffered what Cutcliffe called a “mystifying” lower-leg injury.

Gilbert was a three-star recruit and chose Duke ahead of places like Louisville, Michigan and North Carolina. At first he played poorly, getting burned on a 19-yard touchdown catch by 6-foot-5 wideout Bug Howard. Trubisky threw to Howard in single coverage on a comeback route, and Gilbert went for the ball and whiffed, letting the Tar Heel senior walk into the end zone.

But against one of the best receiving trios in the nation—Howard, Ryan Switzer and Austin Proehl averaged about 200 receiving yards per game combined entering the game—Gilbert held his own in the second half. The Tar Heels only picked up 142 yards in the second half, including 87 through the air, and Duke’s defense stopped giving up the back-breaking explosive plays that have defined its recent losses to North Carolina and struggles closing out wins this year.

“That was a baptism, and some if it was tough,” Cutcliffe said of Gilbert. “But he didn’t panic.”

If Duke’s least experienced starter played his part defensively, then the same can be said about its most experienced player.

Defensive tackle A.J. Wolf—a fifth-year senior who leads the all Duke linemen with 46 games played—forced the game-sealing interception by putting pressure on Trubisky with the Tar Heels down by one at their own 18-yard line with a minute left. The Blue Devils’ leader in sacks, Wolf easily beat Mark Uptegraff, forcing the North Carolina offensive lineman to grab Wolf from behind to prevent a sack. Even with the hold, Wolf still nearly brought Trubisky down.

Duke declined the penalty after the errant throw went straight into the arms of safety Alonzo Saxton II—no North Carolina receiver was even in the vicinity.

“It reminded me of the win we had when I was a [true] freshman,” Wolf said. “That emotion is probably times five because I’ve been here for five years.”

It was a marked turn of events for a defense that has been asked to close games late and come up short.

Against Georgia Tech Oct. 29 and then-No. 23 Virginia Tech Nov. 5, Cutcliffe opted for his offense to punt and let the defense get the ball back late rather than going for it on 4th-and-3 and 4th-and-7.

Those gambles did not work.

But Cutcliffe said those experiences built up his team for Thursday’s game, and he will plant a piece of paper—with a list of areas the team needs to improve in—below the playing surface as a metaphor for the squad’s growth.

“I told [the coaches], ‘If this works—and it will if we do what we’re asked to do—we’re going to plant it out there in that field,” Cutcliffe said. “If you plant it and you fertilize it, it will happen again. You’ll win more close games.”