Will Spradlin had 15 points and McGruder scored 13 to lead the Wildcats (15-4, 4-2), who lost on the road for the first time in four tries.
Kansas State's eight-game winning streak was stopped Wednesday by No. 3 Kansas, which won 59-55 for its 23rd victory in 25 tries at Bramlage Coliseum.
The Wildcats now are on their first losing streak.
Iowa State finally got some breathing room with 5:24 left when Clyburn found Lucious, who stopped under the basket and flipped it back to Melvin Ejim for a two-handed stuff that put the Cyclones ahead 63-56. Clyburn then beat three Kansas State defenders for a rebound on the wing, and Niang turned it into a 3 that made it 68-62 with 2:35 left.
Lucious had 10 points and eight assists for the Cyclones.
Iowa State had an impressive start to the Big 12, rattling off wins over Texas, West Virginia and TCU after nearly beating Kansas in Lawrence in the league opener.
But the Cyclones saw their momentum stunted by Texas Tech, which gave them their first bad loss, 56-51 on Wednesday.
Iowa State responded by being the aggressor early. The Cyclones went on a 10-0 run capped by a nifty underhanded scoop from Niang to go up 24-15. But Kansas State rallied, moving back in front 27-26 at halftime in large part because Iowa State was just 3 of 10 from the free-throw line.