Debutants Adrian Meronk and Ryan Fox settled straight into the WGC-Dell Technologies Match Play with impressive opening victories at Austin Country Club.
Meronk got the better of Kurt Kitayama in Group 10 - where Christiaan Bezuidenhout lost to Tony Finau - while Fox beat Harris English in Group 7 - where Will Zalatoris went down to Andrew Putnam.
Jon Rahm has a job on his hands to get out of Group 2 after a surprise loss to Rickie Fowler while Billy Horschel is in that section looking to repeat his win of two years ago. He tied his opener against Keith Mitchell.
Poland's Meronk, a winner in Australia and Ireland last year, bounced back from losing the first hole by winning the next two and he was ahead until American Kitayama posted a birdie at 13 that tied them with five to go.
It was Meronk who got the job done, securing a 2&1 victory with birdies at the 16th and 17th.
He said: "It was quite stressful. We both played quite good. In order to win the hole, had to hit some great shots, make birdies. It was quite enjoyable and it was very close, but I really enjoyed it.
"I holed a couple of good putts, but I would say my irons were quite solid. My distance control. Overall it was just good balance, so every part of the game was in game. A couple bad shots, bad decisions, but at the end of the day it was just a solid round of golf."
Fox drew first blood against English when he won the fourth hole with a par and he was in charge of the match from then, never surrendering his lead before seeing out a 2&1 success.
The New Zealander, a three-time winner on the DP World Tour, said: "I played really well. There wasn't too many fireworks either way really.
"I think we made a lot of pars, probably both didn't make a whole lot of putts. I capitalized on a couple of mistakes, one on 12 from Harrison and another one on four.
"Then my shot of the day was 13, hitting one to six foot there, and that kind of turned the match, and made a couple nice putts, the one on 13 and the one on 14. Yeah, it was nice to get a win.
"I've played really solid the last almost 18 months. I feel a bit more comfortable playing in these events, playing against the top guys. Coming over here has always been a bit tough because I've kind of only done one week at a time, and I'm in my fourth week over here.
"Played Bay Hill and The Players and played some solid golf, and starting to find some comfort out here, which has been nice. Hopefully I can keep going."
Rahm looked to be following the script when he won the first and third but Fowler took the eighth, the 11th and the 12th to turn the match on its head.
A few three-putts on the back nine from the Spaniard did him no favours and he was shaking Fowler's hand on the 17th after going down 2&1.
In Group 15 Sepp Straka ran into an in-form Corey Conners and went down 6&5 while Cameron Young beat David Thompson.
