STILLWATER, Okla. -- Kansas wasn't satisfied with a clinch.

The No. 1 Jayhawks, despite already wrapping up their 13th straight Big 12 championship earlier in the week, added another statement to an impressive season Saturday, closing out the regular season with a 90-85 victory at Oklahoma State.

Now, and only now, will they reset their focus forward to the Big 12 Tournament and beyond.

"I mean, that's one of the steps and one of our goals and we accomplished it," Kansas forward Landen Lucas said of the regular season. "Now we're moving on to the next one.

"We take the year section-by-section. That was the Big 12 and we did that and now we're looking to go the Big 12 tournament and validate what we did."

What they did Saturday was ride another dominant performance by point guard Frank Mason III, who led the Jayhawks' charge with 27 points, nine assists and eight rebounds, spoiling Senior Night at a sold-out Gallagher-Iba Arena.

In a game where the teams fired big shots back and forth most of the night, Mason was the difference, making repeated winning plays on both ends of the floor.

For Mason, it was extra special, winning for the first time in Stillwater, after losing in his previous three visits to Gallagher-Iba Arena.

"It means a lot to get my first win here," he said, "but it's not all about me; it's about the team and the program. We've been bad for the last three years here and we just wanted to come here this year and change it."

Oklahoma State had a pretty good answer in its own point guard, Jawun Evans, who scored 22 points and added a career-high 15 assists. In the second half, Mason and Evans hooked up often, both willing their teams in a up-and-down game that remained tight to the finish.

Guard Josh Jackson added 17 points and a game-high nine rebounds for Kansas (28-3, 16-2 Big 12), while Jeffrey Carroll led the Cowboys (20-11, 9-9) with 27 points.

"That's about as good and entertaining a basketball game as you could have," Jayhawks coach Bill Self said. "Even if the outcome was different, I would've thought that was a good basketball game.

"I thought they played great and I thought we played well. They made hard shots and certainly Carroll and Evans were fabulous for them. But Frank probably solidified a lot of things today and he was great."

Things such as Big 12 Player of the Year, and perhaps National Player of the Year?

"(Mason) is an unbelievable competitor," Oklahoma State coach Brad Underwood said. "I mean, he just competes. He wills teams. Frank gets going, he makes everybody else so good. And he does it not just on the offensive end, he's their best defender.

"Now, you put 22 years of age, and you put a guy who's had as much game experience as he's had, it's like having Tom Brady at quarterback. Good luck."

After never trailing in the first half, Oklahoma State surged ahead early after intermission, but couldn't hold the momentum, playing catch-up much of the night.

Still, the Cowboys stayed close and pulling within three points three times in the final three minutes.

Both teams play next at the Big 12 Tournament in Kansas City, Mo.

The Cowboys open against No. 24 Iowa State, while Kansas faces the winner of Wednesday's Oklahoma-TCU game.

The Jayhawks led 43-40 at the half after shooting 55 percent from the floor.

Mason led the way with 11 points and forward Carlton Bragg Jr. added nine off the bench. Kansas never trailed in the half and led by as much as 42-30 with 3:41 remaining.

But Oklahoma State closed the half on a 10-1 run behind Evans and Carroll. Evans scored six in the spurt on a 3-pointer and three free throws after being fouled shooting a 3. Carroll scored the other four as part of his 14 points. Evans finished the half with eight points and eight assists.

Kansas didn't score over the final 2:10.

NOTES: Gallagher-Iba Arena, where Bill Self played with the Cowboys, hadn't been so kind to him as the Kansas coach. The Jayhawks had lost five of their seven in Stillwater, including their last three before Saturday, leaving him 4-8 in the arena. ... Oklahoma State celebrated Senior Night with a salute to starters Phil Forte and Leyton Hammonds, the team's only seniors. Forte will end his career as the school's all-time leader in made 3-pointers. He ranks sixth in the Big 12 in career 3s with 326. ... Kansas guards Frank Mason III and Josh Jackson are among 10 semifinalists for the Naismith Trophy, honoring the outstanding college basketball player, as announced by the Atlanta Tipoff Club earlier this week.