The Aggies were anxious to get on the field and bring the focus back to football instead of the school's decision to leave the Big 12. They got things going early, intercepting quarterback Kyle Padron's passes on SMU's first two possessions to jump out to a 14-0 lead.
SMU coach June Jones replaced Padron with backup J.J. McDermott after the early miscues and he helped the Mustangs cut it to 20-14 in the second quarter.
But the Mustangs couldn't do much offensively after that and the Aggies scored 26 straight points the rest of the way to secure the win.
Gray finished with 132 yards rushing. Michael, in his first game since breaking his leg last October, added 85. Tannehill was 21 of 26 for 246 yards. Ryan Swope led Texas A&M's receivers with eight receptions for 109 yards and a score and Jeff Fuller added six catches for 52 yards.
Texas A&M had eight sacks, led by three by Tony Jerod-Eddie, the Aggies most since 2002.
McDermott finished with 254 yards passing and a touchdown, but was sacked seven times. Zach Line ran for 128 yards and a score and 6-foot-8 defensive end Margus Hunt blocked two extra points for the Mustangs. Line had 101 yards rushing with 10 minutes left in the second quarter, but managed just 27 the rest of the way.
The Aggies had built a 33-14 lead at halftime and tacked on a field goal on their first possession in the third quarter to make it 36-14.
Tannehill found tight end Hutson Prioleau on a 32-yard touchdown pass later in the third quarter to extend A&M's lead to 43-14.
The Mustangs trimmed the lead to 20-14 when McDermott found Keenan Holman on a 27-yard touchdown pass on his second drive.
The Aggies finally found an answer for the McDermott-led offense on his third possession and Mustangs had to punt. The Aggies went to Swope on their next drive, hitting him four times for 53 yards, including a 28-yard touchdown to leave it at 27-14 in the second quarter.
Texas A&M sacked McDermott twice on SMU's next drive and the Mustangs had to punt. Michael finished the drive with three consecutive runs, including a 1-yard TD run for the Aggies. Hunt blocked his second extra point attempt of the game, and the Aggies led 33-14 at halftime.
Steven Campbell intercepted a pass by Padron and returned it 51 yards to the to the SMU 6 on the Mustangs' first drive of the game. Michael scored on a 4-yard run two plays later to give Texas A&M a 7-0 lead.
Padron's pass was intercepted on the next drive, this time by Trent Hunter, who returned it 30 yards to give A&M another short field with the ball at the SMU 45. Gray got the Aggies in the end zone to finish that drive with a 5-yard run to make it 14-0.
That's when Jones had seen enough from Padron and replaced him with McDermott. The switch got SMU's offense going, with McDermott orchestrating a seven-play, 60-yard drive fueled by Line's running and capped by a 1-yard touchdown run by the back to cut it to 14-7.
The Mustangs tried an onside kick after that, but it traveled just one yard and sat on the ground for a few seconds before SMU jumped on top of it, giving Texas A&M the ball at the SMU 31.
The Aggies again took advantage of excellent field position when they converted that miscue into another touchdown by Gray, this one on a 2-yard run. Hunt blocked the extra point attempt to leave A&M's lead at 20-7.
Texas A&M's 20 first quarter points were the most it has scored in the opening quarter since Oct. 15, 2005, against Oklahoma State.