Oklahoma coach Lincoln Riley said Murray was with his mother, who was in town, Thursday night and set his alarm wrong. Riley said he has a policy that any starter late to a Friday morning practice doesn't start.
Sophomore Austin Kendall started the first series before Murray entered the game on the second.
"It wasn't anything egregious, wasn't any big issue," Riley said. "Sometimes I set my alarm wrong, too. It happens. He was not very late. It was not a big deal."
After not starting, Murray responded with one of the greatest quarterbacking performances in school history, as the sixth-ranked Sooners routed Baylor 66-33.
Murray's first pass actually went for a touchdown. He went on to complete 17 of 21 passes for 432 yards and five more scores to shatter Jason White's school single-game passing-efficiency record (348.0 to 303.3). Murray also ran for 45 yards and another touchdown to join Baker Mayfield as the only quarterbacks in Oklahoma history to account for seven touchdowns in a game. Both White and Mayfield won Heisman Trophies. Murray came into the weekend fourth in the ESPN Heisman Watch.
"Obviously I was a little disappointed," said Murray, who noted he accidentally set his alarm an hour too late. "For me personally it can't happen.
"But I didn't let it affect me."
Murray and the Sooners face Texas next weekend in the Red River Showdown.