Rory McIlroy's bid for a second WGC-Dell Technologies Match Play title came to a disappointing early end as he bowed out of the group stage in Austin.
McIlroy needed to beat American left-hander Brian Harman to have a chance of reaching the last 16, but gifted his opponent several holes on his way to a comprehensive 5&3 defeat.
The 2015 champion, who came into the event on the back of a victory in the Arnold Palmer Invitational, made a mess of the third, fifth and ninth to fall three down and a conceded birdie on the 10th was matched by Harman from eight feet.
Another Harman birdie on the next extended his lead before he gave McIlroy a glimmer of hope by finding water with his approach to the par-five 12th.
However, while McIlroy could only par the short 13th after attempting to drive the green, Harman pitched to four feet for another birdie and the pair were soon shaking hands on the 15th green.
McIlroy will at least have the consolation of some desired extra time off before stepping up his bid for a first Masters title at Augusta National, which would make him the sixth player to complete a career grand slam.
Harman, who ended the group stage unbeaten with two and a half points from three matches, told PGA Tour Live: "I played really well. I only made one over-par hole and made five or six birdies and was in the fairway and on the green a lot.
"It felt like I was able to put some pressure on the golf course and in match play I feel that's really important.
"You can actually gain a little bit of an advantage if you're first coming into the green and for me I've played with Rory enough times to know that I can't keep up with him off the tee box.
"But I can hit it plenty far to be aggressive into these greens so for me it was about playing my game and hitting the tee shots that I was capable of. He's going to do the crazy stuff he does - the second shot on number six he hit in, I don't have that in the bag. I don't think anybody does."
Harman's win meant he topped the group ahead of compatriot Peter Uihlein, who beat McIlroy on day one and Jhonattan Vegas 4&3 on Friday.