Mike Krzyzewski turned 70 last month. He played college basketball in the 1960s and took his first assistant coaching job in 1974, the year Richard Nixon resigned. Coach K doesn’t look it, but he is old by most measures, except possibly the most important one.

“I felt like a little kid, man,” he said, positively incandescent after Duke’s 81-77 comeback victory over Louisville in an ACC Tournament quarterfinal. “Today was just joy. Obviously, there’s joy of winning, but how you win and to see kids put it all out there, it’s great.”

Barclays Center was home to the very best college basketball had to offer for a gut-churning few hours Thursday, as the fifth-seeded Blue Devils, led by Jayson Tatum and Luke Kennard, made up a 12-point second-half deficit. Their prize? Facing their greatest rival, top-seeded North Carolina, on Friday night at 7.

With fourth-seeded Louisville down by three and six seconds left, the Cardinals’ Quentin Snider took an off-balance three-pointer — falling toward a defender and trying to draw contact — that went wide. Kennard, who had 18 of his 24 points in the second half, made one of two foul shots two seconds later to seal Louisville’s fate.

The Cardinals (24-8) went 15-for-26 at the foul line and missed three in the final three minutes. They also went 4-for-21 from three-point range.

Mangok Mathiang’s jumper ignited a 13-2 Louisville run, good for a 50-42 edge. The Cardinals went ahead 61-49 on Deng Adel’s three-point play. But the Blue Devils (25-8), who seemed deflated, turned out to be anything but. Sparked by Grayson Allen, Duke found its emotional center. Allen had all 18 of his points in the second half and was a pivotal part of a 16-3 run that gave Duke a one-point lead with 8:06 left.

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“I believe in him,” Krz y zewski said of Allen, who was charged with a technical in his previous two games and was scoreless against Clemson in the first round Wednesday. “I love him. And I thought what he did today was sensational. I loved it. He was himself today.”

What’s more, Duke, which was having a fit trying to stop Louisville in transition, moved away from man coverage and into a zone for the second half. The Blue Devils stayed that way until the final seconds, when they knew it would be three-pointer or bust for Louisville.

“Louisville is a Final Four-caliber team with a great coach and great players,” said Tatum, who scored 25. “So for us to play the way we did today after a good win yesterday in less than 24 hours was huge for us.”

The excitement wasn’t lost on anyone, even someone who’s ridden in this rodeo before. Especially someone who has.

Jayson Tatum, left, and Luke Kennard of the Duke Blue Devils celebrate their 81-77 win against the Louisville Cardinals during the quarterfinals of the ACC Tournament at the Barclays Center on March 9, 2017, in New York City. Photo Credit: Jayson Tatum, left, and Luke Kennard of the Duke Blue Devils celebrate their 81-77 win against the Louisville Cardinals during the quarterfinals of the ACC Tournament at the Barclays Center on March 9, 2017, in New York City.

“Holy mackerel, this was a big-time game,” Krzyzewski said. “I’m so happy that I’m a part of it and been a part of it for 42 years, so to have an afternoon like today — I’m 70 years old, and I felt like a kid. I was hugging [Tatum], punching him. He didn’t punch back, which is a good decision on his part. I love that.”