Kansas State (21-8, 13-3 Big 12) became the first team in Big 12 history to finish in last place one year and win the conference the next. The Wildcats finished with a 4-12 conference record last season and tied with Kansas for last place.
The Wildcats, who were picked to finish eighth in the conference by the league's coaches before the season, can do no worse than tie Baylor atop the Big 12 standings. Kansas State will win the title outright if Baylor loses to Oklahoma State on Thursday night.
Lenning went 10-of-17 from the field and 9-of-12 from the free throw line. It was Kansas State's 14th win in the last 15 games between the in-state rivals.
Kansas (15-14, 4-12) lost their fifth straight. The Jayhawks shot only 39 percent from the field and were out-rebounded 37-28.
Kansas State led 27-23 at halftime and pushed the margin to 13 at 48-35 on a layup by Kari Kincaid with just over 12 minutes remaining. But the Wildcats didn't score again for five minutes, letting Kansas back into the game.
A 15-4 Jayhawk run cut the lead to 52-50 with 4 minutes remaining, but Kimberly Dietz hit a 3-pointer to put the Wildcats back up by five. Lenning then converted on a three-point play to push Kansas State's lead to 58-50 lead with three minutes left.
Dietz added 15 points and Marlies Gipson had 10 points and four blocks for the Wildcats.
Danielle McCray led Kansas with 17 points on 7-of-16 shooting, while LaChelda Jacobs, making her first start of the season, added 14 points.
The Wildcats will enter the Big 12 Tournament as the No. 2 seed if they finish tied with Baylor for the regular season crown. Kansas will be either the 10th or 11th seed.