At the end of the first half the SMU Mustangs had a 29-13, and by the end of the third quarter the BYU Cougars was down 38-19. The
Mustangs were suffering from a 20 point deficit with 2:33 left in the fourth quarter. McMahon assisted the Cougars in two quick touchdowns. With 18 seconds left in the game, and the Cougars in possession of the ball at the Mustang’s 41 yard line, McMahon connected with tight end Clay Brown for the touchdown and the tie game. BYU kicker Kurt Gunther kicked the ball through the uprights for the go ahead point to complete one of the biggest comebacks ever in college football.
McMahon was awarded with his second of three Western Athletic Conference Offensive Player of the Year award at the conclusion of the 1980 season. At the end of the ’81 season he was awarded with the Sammy Baugh Trophy, Davey O’Brien Award and was named Consensus All-America. He also placed third in the Heisman Trophy vote. He was chosen by the Chicago Bears in the first round of the 1982 NFL draft and lead the 1985 team to a victory in the Super Bowl.