All-ACC guard K.J. McDaniels scored 18 points on 4-of-15 shooting to help the sixth-seeded Tigers (20-11) earn their second ACC tournament victory since 2008.
Clemson will play No. 7 Duke (24-7), the tournament’s third seed, tonight in the quarterfinals.
Former McEachern High School standout Trae Golden scored 23 points in what was likely his final college game, and Robert Carter Jr. added 13 points for the 11th-seeded Yellow Jackets (16-17).
Daniel Miller sent Georgia Tech to overtime for a second-straight night by hitting a fadeaway jumper that tied it at 55 with 0.9 seconds left in regulation.
Harrison put Clemson ahead to stay when his full-court layup with 44.1 seconds left in OT made it 63-62.
Tech’s Corey Heyward was called for an offensive foul for colliding into Harrison while handing off to Golden with 26.9 seconds left. Harrison hit four free throws in the final 26.1 seconds, sandwiching those sets around a pair from Landry Nnoko, to put the Tigers up 69-62.
Golden then hit a meaningless 3-pointer with 2.6 seconds left for the final margin.
Rod Hall had 10 points for the Tigers, who held Georgia Tech to 37 percent shooting and haven’t allowed a team to reach 70 points in regulation since North Carolina did it on Jan. 26.
McDaniels had to work for his points. He played with a protective strap around his left shoulder and hit 10 of 11 free throws.
Kammeon Holsey finished with 10 points for the Yellow Jackets, who at times appeared gassed late after needing OT to beat Boston College in the first round Thursday night. They went without a field goal for 7 minutes late in regulation in this one before Golden hit a high bank shot to pull them to 55-53 with 55.8 seconds left.
Clemson milked the clock before calling a timeout with 23.9 seconds left, and — after a shot-clock violation was first called, then wiped off by the officials — McDaniels airballed a 3-pointer off an inbounds pass with 19 seconds left to give Georgia Tech one last chance in regulation.
Golden’s drive down the left side of the lane bounced off the rim and off the hands of both McDaniels and Marcus Georges-Hunt and directly to Miller — whose fadeaway jumper swished through with 0.9 seconds left.
Hall’s long baseball pass for McDaniels was broken up by Georges-Hunt as the buzzer sounded to end regulation.
Jaron Blossomgame made two big plays on consecutive possessions to give Clemson its first lead of the second half.
His free throws with 4:15 remaining tied it at 51, and he followed McDaniels’ missed layup with a stickback to put the Tigers up 53-51.
Blossomgame then stretched it to a four-point lead with a jumper with 1½ minutes left.