Defending champion Rory McIlroy edged past 64th seed Thorbjørn Olesen by one hole on the opening day of the WGC-Dell Match Play at Austin Country Club.
Olesen had been on course to beat the World Number Three when he was two up with five to play but a bogey on the last handed victory to McIlroy.
With three European Tour wins under his belt, the Dane started brightly with a birdie on the second and a par on the fourth to lead by two.
Bunker trouble was to follow on the fifth, however, and, although he saved par, McIlroy made a birdie and then added another on the seventh to close the gap in their Group 3 clash.
A birdie and a par would see Olesen regain a one-hole lead at the halfway stage and when the Northern Irishman put his tee shot in the water on the 13th, the lead was two holes.
The four-time Major Champion responded by winning the 14th and 15th and with the match tied on the 18th, a poor chip shot from the rough from Olesen allowed McIlroy to claim the hole and seal victory.
"It was a day where you just sort of had to hang in there. With the wind it's tricky. It swirls around here. It drops, it gusts. It's tough to pick a club," said McIlroy.
"I really struggled with that today. I hit some good shots, but I just had to grind out pars and that's what I did coming in and ultimately that was good enough.
I know if I want to progress further in this tournament, I'm going to have to play better than I did today - Rory McIlroy
The other Group 3 match saw Kevin Na beat Smylie Kaufman 2 and 1.
Branden Grace was beaten 3 and 1 by Chris Kirk in their Group 11 encounter.
Elsewhere in Group 11, Scotland's Russell Knox and Sweden's David Lingmerth halved their match.
Thomas Pieters came back from two down with three to play to halve his match in Group 6 with World Number Six Adam Scott.
The Belgian led by one after four holes but the WGC-Cadillac Championship winner won the eighth and 13th as he looked to have seized control.
But Pieters would claim birdies on the 16th and 17th, which included a 21-foot putt to tie the match, before both saved par on the last hole.
"Two down with three to go, you're thinking half or a win would be a very nice finish. But we both played some good golf. I think a half is good for today," said Pieters.
Chris Wood was beaten by Bill Haas 2 and 1 despite leading through the first nine holes.
In Group 14, Martin Kaymer claimed a one hole win over Shane Lowry as he birdied the 17th and then drove the green on the 376-yard last.
"It was a sensational finish, but the rest was very average, I would say. I didn't hit many fairways today," said Kaymer.
"I couldn't really get the driver going, but I stayed in the game. We gave each other way too many chances. Both of us had chances to really close the match on 14 and 15."
Meanwhile, The Open Championship winner Zach Johnson beat Marcus Fraser 4 and 3 to open his account with a win.
