(Photo credit: Bob Donnan-Imagn Images)

CHARLOTTE -- Duke lost Cooper Flagg to a left ankle injury in the first half, then rallied behind freshman Kon Knueppel to defeat Georgia Tech, 78-70, in the ACC Tournament quarterfinals Thursday.

Knueppel scored a career-high 28 points with eight assists and five rebounds in 39 minutes to power Duke to a 29th win, rallying the Blue Devils from a 14-point deficit in the first half without his freshman co-star. Flagg scored two points and left the game before halftime after injuring his left ankle while gathering a defensive rebound.

Freshmen filled the scoring void with Flagg out. Isaiah Evans and Khaman Maluach both scored 14 points for Duke (29-3), which meet either fifth-seeded North Carolina or fourth-seeded Wake Forest in Friday night's first semifinal game.

Flagg, the potential No. 1 pick in the NBA draft who earlier in the week was named the ACC Player of the Year and ACC Rookie of the Year, was 1-for-7 from the field before he exited not long after Blue Devils forward Maliq Brown reinjured his left shoulder. Brown did not return.

Duncan Powell's 24 points and Baye Ndongo's 15 points led eighth-seeded Georgia Tech (17-16), which shot 42.8 percent from the field. Lance Terry added 12 points.

Duke trailed by five at halftime, its largest deficit at the break this season, but scored the first 12 points of the second half. By the time Jaeden Mustaf scored in a drive, more than five minutes had elapsed in the half.

Duke produced a 19-2 run spanning the two halves.

But Georgia Tech regrouped. The Yellow Jackets closed the gap to 43-40 before another Duke burst that included 3-pointers from Knueppel and Evans that created a 54-43 lead at the under-8 timeout.

The Yellow Jackets' second-offensive woes resembled Duke's troubles in the first half. Georgia Tech managed only 13 points across the first 13 minutes of the second half.

The Blue Devils finished 7-for-30 on 3-pointers, with Evans making four.

Duke trailed 26-12 and started the game 0-for-13 on 3-point attempts. Evans hit a pair of 3s late in the half to help close the gap to 31-26 by the break.

With Brown out and Maluach, the starting center, in foul trouble, the Blue Devils received a boost off the bench from Patrick Ngongba II. Ndongo had 11 first-half points, while no Duke player had more than six.

Duke beat Georgia Tech for the second time this season, though the other came prior to Christmas in Atlanta and without the drama that unfolded Thursday.--Bob Sutton, Field Level Media