Massaquoi hauled in a 4-yard pass from quarterback Matthew Stafford to cap a 12-play, 64-yard drive that gobbled 7:05 off the clock. Stafford and Massaquoi then hooked up on a 2-point conversion play to give the Bulldogs the 3-point lead.
On Georgia Tech's ensuing drive, cornerback Paul Oliver intercepted a pass by the Yellow Jackets' Reggie Ball, and the Bulldogs were able to run out the clock.
"This is a huge win for us," said Georgia coach Mark Richt, who earned his 60th victory. "The last two games (Auburn and Georgia Tech) have been very big. We had a lot of people doubting us and have had a lot of trouble. Everybody stayed strong. Everybody stayed motivated. Everybody stayed together. I will never forget the job they did."
Georgia ends the regular season with an 8-4 mark. Georgia Tech, which will play for the ACC Championship, falls to 9-3.
The Bulldogs now have won six straight games against Georgia Tech and they improved to 58-36-5 in the series. The Bulldogs became the first unranked Georgia team to defeat a ranked Georgia Tech squad.
Georgia's other touchdown came in the third quarter when linebacker Tony Taylor returned a fumble for a score. Ball coughed the football up at the Yellow Jackets' 29-yard line. Taylor grabbed it in the midst of other players trying to recover it and dashed to the end zone. Kicker Andy Bailey added the extra point.
Tailback Kregg Lumpkin paced the Bulldogs with 51 yards, while tailback Danny Ware added 41 yards. Stafford was 16-of-29 for 171 yards and the touchdown.
The game-winning touchdown drive engineered by Stafford was Georgia's longest of the year in terms of time of possession. The Bulldogs also made their first successful 2-point conversion attempt since 2001.
Taylor and linebacker Jarvis Jackson led the Bulldogs with six tackles each. Oliver and the Georgia secondary limited All-American receiver Calvin Johnson to two catches for 13 yards and no touchdowns.
Georgia Tech got a 10-yard scoring run from running back Tashard Choice and two field goals from kicker Travis Bell for its points. Choice rushed for 146 yards on 23 carries. Ball went 6-of-22 for 42 yards and two interceptions.
The Georgia seniors were recognized before their last home game in a pregame ceremony.
"It is hard to swallow a loss right now," Georgia Tech linebacker KaMichael Hall said. "We played our hearts out tonight, one drive there, one drop here, one call there and it is all down the drain. It is not a good feeling right now, especially being a senior. It's a tough loss."