Tannehill had a school-record 449 yards passing and Cyrus Gray ran for two more scores as Texas A&M beat mistake-prone Texas Tech 45-27.
Aggies coach Mike Sherman wouldn't reveal whether Tannehill, the former backup, or senior Jerrod Johnson would start leading up to the game after using both quarterbacks in last week's win over Kansas. Tannehill played the entire game while Johnson, who holds the school record for career yards passing, watched from the sideline.
Sherman played coy again after the game, when asked if Tannehill would remain the starter, saying he just wanted to enjoy the win. But after leading the Aggies to their most points in a conference home game since 2005, it will be difficult to go back to Johnson.
"He did a fine job, there was no doubt he had a very good day," Sherman said of Tannehill. "It's hard to go out there in your first start and I thought he responded very well."
The Aggies (5-3, 2-2 Big 12) trailed 7-0 early, but Tannehill threw three touchdown passes in the first half to give Texas A&M a 24-14 halftime lead. Gray had touchdown runs of 54 and 2 yards in the third quarter to stretch the lead to 38-14.
Tannehill repeatedly credited his teammates when asked to talk about his success on Saturday and said he learned on Tuesday that he would start.
"It was a lot of fun," he said. "Our team came together and we made plays today."
Taylor Potts threw for 227 yards and a touchdown for the Red Raiders (4-4, 2-4). But Texas Tech fumbled twice near the goal line and Potts was replaced by Steven Sheffield in the fourth quarter. Sheffield had 129 yards passing and two touchdowns.
"We're not near good enough to play a game like that and turn it over and have that many penalties," Texas Tech coach Tommy Tuberville said. "We turned it over for two touchdowns and that kind of knocked us out of it."
Jeff Fuller caught two of Tannehill's touchdown passes and finished with 11 receptions for 171 yards to become the second player in Texas A&M history to reach 2,000 career yards receiving.
The Red Raiders opened the second half with a drive that included a 54-yard reception by Detron Lewis. It was halted when Lewis caught an 11-yard pass on the next play and fumbled the ball, which was recovered in the end zone by the Aggies. It was the second time Texas A&M recovered a fumble in their own end zone.
Texas A&M's offense got going in the second quarter with Tannehill finding Michael Lamothe on a 3-yard touchdown pass for a 10-7 lead. Lamothe added a touchdown on a 1-yard reception that made it 45-20 in the fourth quarter.
Fuller's first touchdown was on a 6-yard reception that pushed A&M's lead to 17-7.
Tech cut the lead to 17-14 when Lyle Leong caught a short pass from Potts and dashed untouched into the end zone about three minutes later. Adam James made his first catch of the season on a 12-yard reception on that drive. He took a hard hit on the play that drew a flag on Texas A&M's Von Miller. Former Tech coach Mike Leach was fired in December amid allegations that he mistreated James after he suffered a concussion.
"We started off kind of fast and then we slowed down," Leong said. "We have to get better and keep it rolling on every drive."
Fuller gave the Aggies a 24-14 lead after a 2-yard touchdown catch with 9 seconds left in the first half. That drive was helped by two personal fouls on Tech for targeting defenseless receivers.
Texas Tech jumped out to an early 7-0 lead when Eric Stephens scored on a 1-yard run midway through the first quarter. The Red Raiders took possession after Texas A&M's pass on fourth-and-1 from the Tech 48 was batted down.
Texas Tech forced a fumble by the Aggies on its next possession and was about to stretch the lead to two touchdowns, but Stephens fumbled near the goal line and Texas A&M recovered.
"That was the play of the game," Sherman said. "If they got up 14-0 we might have had to play the game differently."
The Aggies capitalized on that error with a 28-yard field goal by Randy Bullock that cut the lead to 7-3.
Texas A&M running back Christine Michael suffered a broken right tibia on a carry in the third quarter.