Florida trailed 17-10 at halftime after a first half where Texas A&M's offense under new coach Kevin Sumlin pretty much did what it wanted. Things changed in the second half as the Gators clamped down and forced punts each of A&M's six possessions after the break.
Caleb Sturgis helped Florida cut A&M's lead to 17-13 with a 25-yard field goal early in the third quarter.
Florida quarterback Jeff Driskel looked indecisive most of the day and was sacked eight times. But he made a play when he had to, finding Omarius Hines on a 39-yard completion to propel a drive early in the fourth quarter.
Gillislee finished it off, evading a couple of defenders and then tight-roping the sideline on a 12-yard touchdown run to put Florida up 20-17. Gillislee had a 4 yard score in the first quarter.
Driskel also came up big late in the game with a 21-yard run to give the Gators a first down and allow them to run out the clock.
Texas A&M freshman quarterback Johnny Manziel threw for 173 yards and ran for 60 more, but he couldn't move A&M's offense after halftime.
Saturday was Texas A&M's opener after the Aggies and Louisiana Tech postponed last week's game until Oct. 13 because of Hurricane Isaac.
The Aggies' second half offensive woes ruined a great day for their defense. Jonathan Stewart finished with 17 tackles and Damontre Moore had three sacks.
Manziel, who was the first freshman quarterback to start a opener for the Aggies since 1944, looked great early.
A&M's first drive ended with a 27-yard field goal on their first drive.
The Gators soon took a 7-3 lead on a 4-yard touchdown run by Gillislee on their opening drive.
Manziel really heated up on the second drive, using his arm and his feet to move the Aggies down the field. His 11-yard touchdown scamper put A&M back on top 10-7 early in the second quarter.
Then the defense went to work. The Aggies collected three sacks on Florida's next possession and quickly forced a punt.
Texas A&M used a bit of trickery en route to their next score. They went with an end-around receiver pass from Kenric McNeal to Mike Evans to gain 27 yards on second-down. Christine Michael finished off the drive when he took the direct snap and bulled into the end zone for a 1-yard touchdown to extend the lead to 17-7.
Texas A&M's fifth sack of the game forced Florida to attempt a 51-yard field goal in the second quarter. Sturgis missed it, but A&M called a timeout, giving him another shot -- and he nailed the second one to cut the lead to 17-10. It was the seventh field goal of 50 yards or more in his career to set a school record.
Driskel was 13 of 16 for 162 yards and Jordan Reed had five receptions for 59 yards.