For more than 39 minutes, the nation’s most celebrated teenage basketball player demonstrated why dozens of NBA scouts flocked to Atlanta to watch him play.

It wasn’t until the final 20 seconds of Duke’s 77-72 loss to Kentucky that 17-year-old Cooper Flagg finally acted his age.

With Duke’s nine-point lead gone in the second half and the score now tied, Flagg seemed to sense this was his moment. He attacked the 6-foot-2 Andrew Sarr off the dribble, used his body to create space and then began to rise for a mid-range jumper.

Everything was set for Flagg to make a signature basket on the Champions Classic stage, but for one of the first times all night, the Duke freshman couldn’t make it. He never saw Otega Oweh leave his man, allowing the Kentucky guard to poke the ball away, run down the field and draw a foul as he moved forward for a potential go-ahead goal.

Flagg had a chance at redemption after Oweh hit two foul shots, but the Duke freshman lost control of the ball while trying to take Kentucky seven-footer Amari Williams off the dribble. He lay flat on his back in disbelief until two teammates came over to help him up.

That would have been bad enough for Flagg, but it somehow got worse when Kentucky’s Lamont Butler went to the foul line to try to get the win with 5.1 seconds left. Flagg failed to box out Oweh after Butler missed the second of two free throws, squandering Duke’s chance for a final 3-pointer to tie the game.

Flagg finished with a game-high 26 points and 12 rebounds, but his stats aren’t what he’ll remember from the night. What will undoubtedly keep him awake at night are the costly turnovers that capped Kentucky’s comeback from a nine-point deficit in the second half and helped the 19th-ranked Wildcats secure new coach Mark Pope’s first signature victory.

When John Calipari bolted for Arkansas on the eve of last season’s national title game, Kentucky athletic director Mitch Barnhart responded by making two big swings. He made Dan Hurley say no, and the UConn coach quickly opted to chase a three-peat in Storrs. He then offered the job to Scott Drew and flew to Lexington with his family, but the Baylor coach decided to pass on the opportunity.

The less than stellar “Plan C” that Barnhart focused on has so far proven to be an inspired third choice. Pope is one of Kentucky’s team captains, team captain of Rick Pitino’s powerful 1996 national championship team and the first ex-Wildcat to coach his alma mater since 1985. He is also in many ways the anti-Calipari, an innovator who created a modern, 3-point-heavy offence.

The veteran-heavy roster that Pope put together on the spot bears little resemblance to Calipari’s freshman-laden teams. The Wildcats have nine transfers, including six fifth-year seniors. Their players have made 586 starts combined, even though they had little time to play together.

Experience mattered Tuesday night as Duke extended its lead to 56-47 with 13 minutes left in the second half. Instead of withering, Kentucky increased its defensive intensity, allowing the Blue Devils to make just five field goals the rest of the way.

Tyrese Proctor and Kon Knueppel were strong in support of Flagg in the first half, but both succumbed to Kentucky’s relentless pressure after halftime. That left Flagg as Duke’s primary initiator and playmaker, which was a lot to ask of a 6-foot-1 teenager playing in his first collegiate game.

For a while, Flagg prospered. He shot 9-of-19 from the field, made smart decisions with the ball in his hands and showed the athleticism, versatility and competitive fire that made him the presumptive No. 1 pick in next year’s NBA Draft.

On one possession, he blocked a shot, led the fast break and drew a foul on the other end. On the other end, he beat every slow-reaction Kentucky transition defender all over the floor, with his hustle earning a 2-on-1 fast break, an uncontested dunk and an immediate Kentucky timeout.

The final seconds were a sour ending for Flagg.

All too abruptly, a signature performance became a learning experience.