Thorbjørn Olesen got off to an excellent start at the WGC-Dell Match Play to go one up after five holes against defending champion Rory McIlroy.
Olesen is the 64th seed at Austin Country Club but is a tough customer with three European Tour wins to his name and the Dane made 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 his par, McIlroy made a birdie to close the gap in their Group 3 clash.
In the other Group 3 match, Kevin Na was one up through four holes against Smylie Kaufman.
Shane Lowry and Martin Kaymer were all square in Group 14 after five holes, while Zach Johnson was one up against Marcus Fraser a hole ahead.
In another match between two European Tour Members, Andy Sullivan was four up against Bernd Wiesberger having played ten holes, with the Austrian looking out of sorts as he made five bogeys.
Louis Oosthuizen was all square through 12 holes against Matt Jones in the other match in that group.
Frenchman Victor Dubuisson, runner-up at this event in 2014, had four birdies on the front nine as he moved two up against Justin Thomas in Group 1, while Ryder Cup team-mate Jamie Donaldson was three down after ten holes against World Number One Jordan Spieth.
Swede David Lingmerth was one up on WGC-HSBC Champions winner Russell Knox through eight holes while Branden Grace was one down against Chris Kirk in the other Group 11 match-up.
Chris Wood made a strong start to lead Bill Haas two up in Group 6 after seven holes, with Tomas Pieters and Adam Scott all square with 11 to play.
Among the latest starters, Danny Willett was all square with Jaco van Zyl after three holes in Group 10, with Justin Rose also level with Fabian Gomez in Group 7 where Anirban Lahiri dropped the first against Matt Kuchar.