Ephraim Tshimanga’s steal and subsequent layup with 4:10 in the third quarter gave Allatoona (9-0) a 46-28 lead. But Justice Morgan and Brandon Powell combined to score 24 points in the fourth quarter to rally Harrison (4-8) and force the extra period.
Morgan scored 14 of his 27 points in the fourth, while Powell, who also finished with 27, scored 10 points in the fourth.
Allatoona was only 1-of-12 from the free-throw line in the final 8 minutes of regulation, after holding a 55-43 lead at the end of the third period.
Rodney Brown, who had 15 points for Allatoona, scored off a layup with 5:22 remaining in the game to put the Buccaneers in front 63-50, and his dunk with 2:30 left gave Allatoona a 10-point lead.
A jumper from Morgan and consecutive 3-pointers from Powell and Jack Forrest left Harrison trailing 69-67 with 1:20 on the clock.
After Bradley Brevet’s layup with 36.2 seconds left put Allatoona on top 74-67, a layup from Morgan and putback from Nick Hughes left Harrison trailing 74-71 with 7.7 seconds remaining.
Daniel Fowler was fouled on Allatoona’s next possession, but he missed both free throws. Tony Patrick recovered the second errant shot for Harrison and Morgan was fouled while shooting a 3, sending him to the line with 1.1 seconds left in regulation.
Morgan made all three free throws to tie the contest at 74, and Hughes’ steal prevented the Buccaneers from getting a final shot off.
Harrison, which made 12 3-pointers as a team, couldn’t find its outside stroke in overtime, and Fowler, who finished with a team-high 25 points, made several big blocks, picked up steals and assisted on several baskets to help the Buccaneers pull away late.
Fowler’s jumper gave Allatoona an 80-76 lead, and his block and assist on Brown’s layup put the Buccaneers in front 82-76 with 1:50 remaining.
Another steal and assist led to Brevet converting a three-point play, and Fowler’s jumper with 1:10 capped a 9-0 run that gave Allatoona an 87-76 margin with 1:10 left.
After shooting poorly from the free-throw line in the fourth quarter, the Buccaneers found their stroke in overtime, going 7-of-9.
Ephraim Tshimanga finished with 16 points, 10 rebounds and four assists for Allatoona, while Brevet finished with 15 and Trey Tshimanga 13. Fowler also had 14 rebounds and 10 assists to complete a triple-double.
Hughes had eight points and 14 rebounds for Harrison. Morgan tallied six assists.
“Harrison is a good team that shoots the 3 really well,” Allatoona coach Markus Hood said. “I told the kids, (Harrison) is never out of a game, and they proved that (Friday). My hat goes off to them.
“I thought our kids did a great job down the stretch to get their composure back. We missed free throws down the stretch that could have sealed the deal, but I’m so proud of our team for letting loose and attacking again in overtime.”
Allatoona will play Cartersville tonight in an 8:30 p.m. semifinal. Harrison dropped into the losers’ bracket where it will face Pope at 2:30 p.m.