The Wildcats (15-2, 2-1 Big 12) handed the Buffs their first loss at the Coors Events Center in 10 games this season. The Buffaloes hadn't started 10-0 at home since the arena opened in 1979-80.
Cory Higgins scored a season-best 30 points for Colorado (10-7, 1-2), which upset Baylor on Tuesday night and was seeking to beat ranked teams in consecutive games for the first time in the program's history.
The Buffs hung with the Wildcats all game but were ultimately done in by fouls and a lack of rebounding. The Wildcats were 38 of 54 from the free throw line, compared to Colorado's 27 of 40, and they outmuscled the Buffs with a 40-19 edge on the glass.
Kansas State began to inch ahead midway through the second half after Austin Dufault missed the front end of a 1-and-1 for Colorado that would have tied it at 52. Wally Judge made two free throws, Victor Ojeleye hit a hook shot and Rodney McGruder swished two foul shots after a steal to give Kansas State a 58-51 lead.
The Wildcats maintained their lead the rest of the way, with the Buffs cutting it to 78-74 on a basket by Marcus Relphorde, who finished with 18 points.
But they couldn't get any closer.
As the Wildcats wrapped up their win in the final seconds, NBA star Chauncey Billups, a Colorado alum, got up from his courtside seat and made his way through the tunnel, where he waited for coach Jeff Bzdelik and then went into the locker room to talk to the team.
The Buffs were coming off the 78-71 upset of No. 22 Baylor on Tuesday night, their first win over a ranked opponent since Feb. 15, 2007.
The Wildcats looked like they were going to put a quick end to the Buffs' hopes of another upsets of a ranked team when they took a 9-2 lead in the opening minutes. But Colorado adjusted and twice grabbed the lead in the first half before heading to the locker room down 38-34.
Colorado freshman sensation Alec Burks scored 14 points but had just four after halftime.