The Wildcats, given no chance by most experts, also got 235 yards rushing by Darren Sproles.
"It was all about the offensive line," said Sproles, who set a Big 12 championship game rushing record. "I have to give credit to the offensive line."
Kansas State (10-4) clinched the first Big 12 title in school history and threw the oft-maligned BCS into chaos. It likely will get even more ridicule if Oklahoma gets a spot in the national championship game after it didn't even win its league and was beaten in its conference title game by a three-loss team.
The Wildcats dominated the contest and score 21 points in the third quarter. The Sooners did not have a point in the last 57 minutes.
"Knocking off OU, the No. 1 team, nobody ever thought we'd do it," said Roberson, "and getting into the BCS for the first time ever."
Kansas State won its first league title of any kind since capturing the Big Six Conference crown in 1934.
The title game will be played at the Sugar Bowl on Jan. 4. The participants will be announced Sunday evening.