Allen threw for 322 yards and two touchdowns to help No. 14 Texas A&M remain undefeated with a 30-17 win over No. 21 Mississippi State.
The Aggies (5-0, 2-0 Southeastern Conference) led by 14 at halftime. They didn't score a touchdown in the second half, but added two field goals and forced two turnovers to secure the victory.
"It was a really good job by our defense to pick us up when we were down and we needed it," Allen said.
Now the Aggies get a week off to recuperate before hosting No. 13 Alabama in two weeks.
Dak Prescott capped a 68-yard drive with a 5-yard touchdown run that got Mississippi State (3-2, 1-2) within 27-17 with about 12 1/2 minutes remaining.
A 30-yard field goal by Taylor Bertolet pushed the lead to 30-17 midway through the fourth quarter.
Allen threw touchdown passes of 1 and 29 yards in the first quarter and Tra Carson ran for a score in the second to help A&M to the win.
Prescott threw for 210 yards and ran for 96 more.
"All the little things you have to do to win a game we didn't do them tonight and you're not going to win that way," Mississippi State coach Dan Mullen said. "It's just not going to happen."
Garrett had seven tackles, two tackles for losses, including a sack, forced a fumble and batted down a pass to lead A&M's defense. He has 7 1/2 sacks this season. Coach Kevin Sumlin has been impressed with the way Garrett has responded to being double- and triple-teamed this season.
"It's easy to get frustrated if you're him," Sumlin said. "I think that's where he's growing. Last year he got frustrated and he showed it, this year's he's growing up mentally and hangs in there and keeps going."
Daeshon Hall added a sack for the Aggies to give him five this season when he shed a blocker and took down Prescott for a five yard loss in the second quarter.
Garrett and Hall both broke into huge grins when asked how much fun it is to play together.
"It's a race to the quarterback every time," Garrett said.
Allen had to work for more than half of the game without starting receiver Ricky Seals-Jones, who was ejected for targeting midway through the second quarter.
The 6-foot-5, 240-pound Seals-Jones leveled 5-11 safety Brandon Bryant with a hit to the head on a passing play by A&M. As he left the field, Seals-Jones jumped around in front of the crowd waving his arms and received a loud ovation.
Seals-Jones took to Twitter late in the game, retweeting a tweet that questioned the call on his hit and included a video of it.
Sumlin wasn't aware that Seals-Jones had tweeted when asked about it after the game. He said they do have rules that forbid tweeting during games.
"We'll address that," he said.
Prescott extended his streak of passes without an interception to 225. The nation's longest such streak almost came to an end early in the fourth quarter when Garrett tipped one of his passes at the line and Brandon Williams came just short of grabbing it.
Fred Ross had 11 receptions for 103 yards for his third career 100-yard receiving game for Mississippi State.
Texas A&M's offense stalled on the ensuing drive and the Aggies settled for a 24-yard field goal that made it 27-10.
The Bulldogs were driving again on their next possession when Garrett tackled Aeris Williams, causing a fumble which A&M recovered on its own 3.