Kansas State (16-2, 3-1 Big 12) smothered Texas with its extended man-to-man defense to overcome a 1-for-12 effort from 3-point range and held on to beat a No. 1 team for the third time in school history.
Curtis Kelly scored 17 points and freshman Rodney McGruder chipped in 11 key points for the Wildcats, who used a late 11-1 run to take control in their record 14th straight win at Bramlage Coliseum.
Texas (17-1, 3-0) trailed by 14 points in the first half, made a run early in the second, couldn't keep it going in its second week ever at No. 1. The loss leaves No. 2 Kentucky (18-0) as the lone unbeaten team in Division I.
Avery Bradley had 11 points for the Longhorns, who shot 36 percent from the field following a season-low 35 percent against Texas A&M.
Texas had passed every test on the way to its first No. 1 ranking.
The Longhorns beat North Carolina at Cowboys Stadium, Michigan State in Austin, and pulled out a tougher-than-expected road win against Texas A&M-Corpus Christi. It was a tough first week as the nation's top-ranked team against Iowa State and Texas A&M, but Texas still won both.
Monday's game represented the Longhorns' toughest task so far: on the road in a juiced arena against a top 10 team.
They didn't seem ready for it.
Uncharacteristically frazzled, Texas struggled against Kansas State's pressure and its own indecisiveness, shooting 10 of 33 from the field with 11 turnovers to trail by 10 at the half.
Kansas State fans were certainly ready, lining up outside Bramlage Coliseum hours before the game, many sporting fake Abraham Lincoln beards - a school giveaway - and "Fear the Beard" T-shirts in homage to the fuzzy growth under junior guard Jacob Pullen's jaw line.
Pullen joined in the fun, too, trotting out to warmups with a faux Lincoln before revealing the real thing.
The Wildcats fed off the facial-fuzz energy early, using their aggressive defense to hound the Longhorns into turnovers and difficult shots.
Texas managed to keep it close for a little while before Kansas State put together the kind of run the Longhorns usually snuff out opponents with: 18-4.
Samuels was the key, slashing inside on drives and putbacks, capping the spurt with a 3-pointer that put the Wildcats up 36-22.
Of course, being the top-ranked team in the country, Texas had an answer, scoring eight quick points in the second half to cut a 10-point deficit to 36-34.
A back-and-forth battle followed until Kansas State went on the 11-1 run to go up 62-52, then set off pandemonium in the Little Apple by hitting just enough free throws down the stretch.