The Bears were trailing 25-21 after the Wildcats had reeled off 15 straight third-quarter points, but Petty's third touchdown toss of the game put Baylor (5-0 Big 12, 2-0) ahead to stay.
Petty completed 12-of-21 passes for 332 yards without an interception, while Reese compiled five catches in all for 184 yards, including two scoring receptions.
Antawn Goodley hauled down four passes for 129 yards with a score and Glasco Martin ran for 70 yards with a fourth-quarter touchdown on 16 carries for the winners.
Quarterback Daniel Sams ran for three touchdowns, racking up 199 rushing yards on 30 carries for KSU (2-4, 0-3).
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