The Wildcats (8-2) could never shake the Tigers (1-10), who trailed by just six points with 1:13 remaining. But four free throws in the final 35 seconds protected Kansas State's lead.
A 7-0 run by the Wildcats -- five of the points were by McGruder -- gave them a 46-36 lead with 15:03 remaining. It was the first double-digit advantage of the game.
The lead grew to 53-38 with 12 minutes to play. But Texas Southern went on a 10-2 spurt that included 3-pointers by Penn and Gibbs.
With 7:40 left, Texas Southern trailed 55-48 and hung in until the final minute.
Former Kentucky guard Ed Davender, the only Wildcat with at least 1,500 points and 400 assists, has died. He was 49.
Guard Naz Mitrou-Long, whose 2015-16 season ended in December due to hip problems, has been granted a hardship waiver for the coming season, Iowa State said.
As the Sooners look to life without superstar Buddy Hield and his sidekicks, it's clear their unseasoned players will need to grow up fast.