LAWRENCE, Kan. -- The odds were stacked against Oklahoma State.
No. 2 Kansas was on an 18-game winning streak and undefeated in the Big 12.
In addition, the Jayhawks on Saturday were in Allen Fieldhouse, where they had won 33 straight and beaten the Cowboys 16 consecutive times dating to 1990.
Well, upsets do happen. Markel Brown scored 28 points and Marcus Smart added 25 as Oklahoma State stunned Kansas 85-80.
The upset was such a thrill that Smart did two back flips during the postgame celebration. The acrobatic display was impressive considering Smart, who had two crucial stickbacks for back-to-back buckets with 2:19 and 1:32 left, packs a solid 225 pounds on his 6-foot-4 frame.
"It's just second nature for me to do that and it just came to my head," said Smart, who also turned back flips after his high school team from Flower Mound, Texas, captured a state championship.
That was when Smart drew national attention as a college prospect and strongly considered Kansas before signing with Oklahoma State. In addition to scoring 25 points, Smart added a game-high nine rebounds, including eight on the offensive glass.
"He definitely whipped our guards," Kansas coach Bill Self said. "That was a physical beatdown."
The Cowboys (15-5, 5-3), the best free shooting team in the Big 12 with a .751 percentage, went 10 of 12 from the line in the final 1:12 to salt the victory.
The first of those trips was by Smart, who nailed two free throws to give Oklahoma State a 75-68 margin. Kansas (19-2, 7-1) still crawled as close as 81-80 on a drive by Elijah Johnson with 18 seconds left, but the senior guard then committed a turnover on the Jayhawks' last possession when they were down by three.
"I've known all along that we haven't played as well as what our record indicated," Self said. "The game was a primary example of a team coming out and getting comfortable. Oklahoma State hadn't won a on the road in a long time. They came out, got comfortable and wanted to beat us so bad. We didn't have the same desire."
The road win was the first of the season for the Cowboys. They had lost eight straight on the road dating to last season, as well as 22 of their previous 23 road games in the Big 12.
The Jayhawks, who were led by freshman guard Ben McLemore with 23 points, actually recovered from a 14-point first-half deficit to go ahead by four. They still held that margin after a 3-pointer by Naadir Tharpe with 7:10 remaining.
"A lot of teams that get big leads in here and then lose it in the second half rarely come back," Oklahoma State coach Travis Ford said. "That's probably the biggest thing I was proud of ... we stayed positive."
Brown started on fire, hitting his first five attempts from 3-point range and netting 22 first-half points. That led to a 40-34 lead at the break.
The margin could have been more. Oklahoma State led by as many as 14 as Smart added 10 first-half points. The Jayhawks scored just one field goal in a span of seven-plus minutes before McLemore created on a nifty drive for a bucket with 9:13 left.
Senior center Jeff Withey led Kansas with nine first-half points, despite getting tagged with two fouls and playing just 12 minutes. Withey finished with 11 points and a team-high eight rebounds.
The Jayhawks committed 16 turnovers, including four by Johnson, who also distributed a game-high six assists.
The home loss was just the eighth for Self in his 10 seasons as Kansas coach.
"With this league race, all we did was invite everybody back into it," Self said. "It's a joke what we did. Hopefully, we can regroup. It's not panic mode or anything like that. ... Let's just call it like it is: We are mentally tough in some ways, but physically this is our softest group of all time."
NOTES: Oklahoma State matched its 2011-12 win total with the victory against Kansas. ... The game was the third for Phil Forte since the freshman guard changed his OSU uniform number from 10 to 13. He has scored 54 points in that stretch. He grew up a Kansas fan since his father, Phil Forte Sr., played football for the Jayhawks. ... Withey had three blocks, boosting his career total to 254, four short of the Kansas career record held by Greg Ostertag. ... Kansas senior guard Travis Releford failed to score in double figures for the first time in 18 games. ... The last team to beat Kansas in Allen Fieldhouse was Texas on Jan. 22, 2011.