Petty threw for 161 yards and accounted for three touchdowns while playing the first half of the Bears' 45-0 victory over Southern Methodist.
Petty, the reigning Big 12 offensive player of the year, was held out in the second half because of a bruise to his lower back. He moved gingerly at times and often grabbed as his lower back and side between plays after taking an early shot.
Baylor led 24-0 after the first quarter, including TD drives six yards after an SMU fumble and four yards after Levi Norwood's 45-yard punt return.
SMU's three quarterbacks were sacked a combined eight times. The Mustangs were held to 67 yards.
Justin Worley threw for 273 yards and three touchdowns to help host Tennessee beat Utah State, 38-7, in a game matching two quarterbacks returning from injuries that ended their 2013 seasons prematurely.
Worley completed his first 13 passes of the second half in his first appearance since missing Tennessee's final four games last season with an injured right thumb. He completed 27 of 38 passes.
Worley outperformed Utah State star Chuckie Keeton, who was playing for the first time since tearing the anterior cruciate and medial collateral ligaments in his left knee last October. Keeton went 18 for 35 for 144 yards and a touchdown with two interceptions.
In a late game Saturday night, Marcus Mariota threw for 267 yards and three touchdowns then ran for one more before sitting out the second half, leading the No. 3 Oregon Ducks to a 62-13 victory over South Dakota in Eugene.
Running back Byron Marshall was Oregon's top receiver with eight catches for 138 yards and two touchdowns for the Ducks, who have won 10 straight home openers. Freshman Royce Freeman ran for 75 yards and two scores.
Mariota's 62-yard touchdown pass to Dwayne Stanford on Oregon's first series of the game gave him the Ducks' career record for touchdowns with 79 (64 pass, 14 rush and one reception), surpassing Joey Harrington.
In another late game Saturday, John Ross scored on a reverse and a 91-yard catch and No. 25 Washington held off Hawaii, 17-16, in Honolulu in Coach Chris Petersen's debut with the Huskies.
Jeff Lindquist threw for 162 yards in his first start for Washington after Cyler Miles was suspended for the game for his role in an off-season fight. But most of Lindquist's total came on the big play to Ross. He completed three of 15 passes for 28 yards in the second half.