Playing their first game outside the top 10 since November 2007, they spent half the night proving they deserved their drop before Hood helped them pull away for their 25th straight win at Cameron Indoor Stadium.
Marcus Georges-Hunt scored 18 points for the short-handed Yellow Jackets (9-6, 0-2), who shot 49 percent yet lost their second straight.
Duke had trouble getting any sort of separation until Hood hit 3-pointers 45 seconds apart down the stretch.
Hood — who made all five of his 3s in the second half — hit a stepback 3 one possession before knocking down one with a hand in his face to put the Blue Devils up 66-50 with 6½ minutes remaining.
Daniel Miller added 14 points for Georgia Tech.
The Yellow Jackets were outrebounded for the first time this season on the same day the ACC's top rebounder — Robert Carter Jr., who averages 9.3 boards— had surgery on the meniscus in his left knee. He has been out since tearing it Dec. 29.
The Blue Devils struggled for much of the game to slow down a Georgia Tech offense that entered 12th in the 15-team ACC in both scoring and field goal percentage, averaging 71 points and making under 43 percent of its shots.
The only thing resembling a Duke run came early in the second half when Sulaimon's 3-pointer capped a quick 12-3 burst that gave the Blue Devils their first double-figure lead, 48-38, with 16½ minutes left.
Duke's streak of 225 consecutive games as a top 10 team came to an end shortly after a 79-77 loss at Notre Dame that sent the preseason ACC favorites tumbling down the rankings.
Early on, it didn't seem to help.
The Blue Devils led 34-33 after sleepwalking through a first half in which they allowed Georgia Tech to shoot nearly 54 percent.
The struggles continued for Parker, a 20-point scorer in 10 of his first 12 games who found himself benched late in the Notre Dame loss following a 2-for-10 shooting performance. His only two field goals in the first half of this one were dunks, and he didn't hit a jump shot until midway through the second half.