Jason Kokrak upstaged Jordan Spieth, outlasting the former world number one to lift the Charles Schwab Challenge trophy.
Spieth carried a one-stroke lead into the final round at Colonial Country Club, where the three-time major champion was looking to add to his 2016 triumph.
But Kokrak had other ideas and shot a 70 to prevail by two shots as Spieth faltered via a three-over-par 73 in Fort Worth, Texas on Sunday.
Kokrak mixed two birdies with three bogeys over the first seven holes, though a run of three birdies over a six-hole stretch from the eighth to the 13th fuelled the American.
The victory made Kokrak the first player over the age of 35 to win his first two PGA Tour titles in the same season since Italian Francesco Molinari achieved that feat – which included an Open Championship triumph – in 2018.
Spieth made a slow start behind three consecutive bogeys from the second to fourth holes before responding with birdies at the sixth and ninth, but he found water at the 18th, having bogeyed the 15th.
Kokrak – who finished 14 under – earned a second victory from his last 17 starts following the 36-year-old's success at the CJ Cup earlier this PGA Tour season.
Charley Hoffman (65), Patton Kizzire (67), Sebastian Munoz (68) and Ian Poulter (68) ended the tournament four shots off the pace in a tie for third.
Jordan Spieth's approach shot finds the water on 18. pic.twitter.com/qbEoQM1DQM— PGA TOUR (@PGATOUR) May 30, 2021
Defending champion Collin Morikawa's bid for back-to-back titles resulted in a share of 14th position at five under after he posted a final-round 68.
Former world number one and 2013 U.S. Open champion Justin Rose (71) and Sergio Garcia (76) – the 2017 Masters champion and 2001 winner of this event – finished in a tie for 20th, 10 strokes behind Kokrak.