Jason Day was 3 up with four holes to play, an ideal start to the Dell Match Play that included five birdies and hardly any stress.
And then he felt his back tighten on a tee shot at the 15th hole.
It stung so badly on his next tee shot that Day grabbed his back and winced. He stepped gingerly into a bunker. When his short par was conceded, he took a knee. Exactly what happened was not entirely clear because Day immediately sought treatment and left without speaking. But with a long week ahead of him at Austin Country Club, and the Masters just two weeks away, this victory surely felt hollow.
Without much drama on the golf course because of tough greens and Texas wind, Day supplied it with the latest in a long list of injuries.
Jordan Spieth, a crowd favorite who helped the University of Texas to a national title in 2012, produced what the crowd came to see. The No. 1 player built an early lead, made a few pivotal putts to stay in control and beat Jamie Donaldson of Wales 3 and 2.
Rory McIlroy escaped with a victory. He never led until winning on the 18th hole when Thorbjorn Olesen shanked a chip. Martin Kaymer rode the wind and drove the green on the 376-yard 18th hole to wrap up a 1-up victory over Shane Lowry. Matt Kuchar had the shortest day, dispatching Anirban Lahiri in 13 holes.
Day overcame an early deficit and had the match in hand when he first felt pain. The severity of the injury was unclear. Day left without speaking to reporters, and his agent later sent a statement that he tweaked his back, had some work done on it, was pleased with winning and is getting prepared to play Thursday.
Rickie Fowler, the No. 5 seed, rallied from 3 down on the back nine to square his match on the 15th hole, only for Jason Dufner to win the next two holes with birdies to beat him on the 17th hole. He was the highest-ranked played to lose.
Dustin Johnson (No. 8) lost to Robert Streb, and Hideki Matsuyama (No. 12) lost to Rafa Cabrera-Bello. Adam Scott (No. 6), who has lost seven straight matches in this event, had to settle for a halve with Thomas Pieters of Belgium.
Players and caddies wore black ribbons in their caps to honor the victim of Tuesday's bombings in Brussels.
