Josh Jackson had 23 points and 10 rebounds for Kansas. Frank Mason III added 19 points, including two free throws to seal the win, and Devonte Graham scored 13 as the Jayhawks (20-2, 8-1) pulled a game ahead of the Bears (20-2, 7-2) in the Big 12 race.
It was nip-and-tuck almost the entire way.
The game was tied 64-all with 2:23 left when Jackson went baseline for a dunk. After Mason made a couple of foul shots moments later, the teams began trading baskets down the stretch in a matchup that lived up to its billing.
Lecomte's fall-away jumper brought Baylor to 70-68 with 51 seconds left, but Ish Wainwright missed a 3-pointer badly on the team's next possession. Svi Mykhailiuk made one of two free throws with 18 ticks left for the Jayhawks, then they buckled down for the biggest stop of the night.
Lecomte was hounded around the perimeter by Mason and Landen Lucas, and passed it off to Motley, who likewise had nowhere to go with Jackson in his face. Motley's pass landed out of bounds with 1.3 seconds left, and Mason made both free throws after getting fouled on the inbounds play.
Mykhailiuk finished with 11 points for the Jayhawks, who hung on to win their 51st consecutive game at Allen Fieldhouse - a building where Baylor has never won in 15 tries.
Motley led the Bears with 16 points and 10 rebounds. Lecomte also finished with 16 points.
The Jayhawks dominated the opening minutes, getting off shots before Baylor could settle into its vaunted zone. But they eventually got too sped up, turning it over three straight times.
Gradually, the Bears were able to slow the game to their liking, clawing back to take their first lead at 18-16 midway through the half. They proceeded to rip off a 10-2 run a few minutes later, their big salvo triggered by a defense that completely shut down the Jayhawks in the paint.
Motley began to assert himself at the other end, scoring most of his 14 first-half points right at the basket, as the Jayhawks' poor interior play continued to drag them down in the second half.
It was their outside shooting that kept them in the game.
Mykhailiuk drained two 3-pointers in quick succession out of the locker room, part of a 13-0 run that gave the Jayhawks a 41-36 lead. Mason added five points during the charge, which energized another sellout crowd at the Phog and prompted Baylor coach Scott Drew to call a timeout.
Baylor is hardly out of the conference race. Its two Big 12 losses have come at West Virginia and Kansas, and there is no harm in that. The challenge going forward is to beat those teams at home.
Kansas nevertheless took a big step toward winning its 13th straight league title, and did it by beating the Bears for the ninth straight time. Jayhawks coach Bill Self improved to 8-0 against top-5 teams in Allen Fieldhouse.
Baylor returns home to play Kansas State on Saturday.
Kansas welcomes Iowa State to the Phog on Saturday.