West Regional No.1 seed Kansas were eliminated from the NCAA tournament after a nail-biting 72-71 round-of-32 loss to Arkansas on Saturday.
The Jayhawks join Purdue as the second No.1 seed to be bundled out of the March Madness tournament in consecutive days, after the Boilermakers lost to No.16 seed Fairleigh Dickinson on Friday.
Multiple No.1 seeds missing the Sweet 16 had only occurred three times since the NCAA expanded in 1985 prior to this week.
Kansas led 35-27 at half-time but the Razorbacks produced a strong second-half rally, with guard Davonte Davis scoring 25 points with eight rebounds.
Razorbacks guard Ricky Council IV added 21 points with six rebounds and four assists, while Jalen Wilson top scored for Kansas with 20 points and four rebounds.
Arkansas' win is their third consecutive victory in the round of 32, setting up a Sweet 16 clash with either Saint Mary's or UConn. The Razorbacks toppled No.1 seed Gonzaga last year.
"I've been coaching a long time and that's as great of a win as I've ever been a part of because of the history of Kansas," Arkansas coach Eric Musselman said. "A lot of people didn't think we were going to win our first-round game."
Elsewhere, Midwest Regional No.1 seed Houston avoided Kansas' fate with an 81-64 win over Auburn led by Tramon Mark with 26 points and nine rebounds.
South Regional No.1 seed Alabama also eased into the Sweet 16 with a 73-51 triumph over Maryland with Jahvon Quinerly top scoring with 22 points for the Crimson Tide.
UCLA won 68-63 over Northwestern, Tennessee edge Duke 65-52, San Diego State beat Furman 75-52, Texas toppled Penn State 71-66 and No.15 seed Princeton beat Missouri 78-63.