Russell Knox started the WGC - Dell Technologies Match Play in terrific form as he secured a 3 and 2 win over Bill Haas at Austin Country Club.
Knox - playing in just his second European Tour event of the season - did not drop a shot on his front nine as he piled the pressure on his American opponent in the early exchanges of his Group 11 match.
The Scotsman opened up in the best possible way after a par on the first to go one up before extending his lead on the third with another par after Haas carded a bogey.
Haas halved the deficit with a wonderful chip to within a foot to pick up his first birdie on the sixth but Knox restored his two up advantage with his first gain of the round after sinking a 15-foot putt on the ninth.
Knox made it successive birdies on the next when his approach landed six feet from the pin to go three up, and despite a bogey on the 12th to down a shot, he confirmed victory with a birdie on the 16th.
“I was really happy the way I played today. I haven't been playing as well I would like recently. I came out today and drove the ball beautifully,” Knox said.
“I love this place. The front nine and the back nine are completely different. But you've got to be in the fairway. That's one of my biggest strengths, is getting in play and then my iron play can take over.
“It's crucial to get off to a good start and gain some momentum and see if you can keep it going.”
K.T. Kim was victorious over 2016 Masters Tournament champion Danny Willett following a 3 and 2 win in the other Group 11 encounter.
It's crucial to get off to a good start and gain some momentum and see if you can keep it going - Russell Knox
Kevin Na stormed to a 5 and 4 success against Matthew Fitzpatrick as he dominated their all-European Tour Group 6 clash.
A Fitzpatrick bogey on the first was enough for the American to develop his lead before he extended it to two up at the third when he picked up his first birdie of the round.
A fantastic run of eagle-birdie-par on the sixth, seventh and eighth transformed Na's lead to five up but Fitzpatrick hit back with birdie from eight-feet on the 12th before the Englishman relinquished that gain with a blemish on the next as Na restored his five up advantage to see out the win.
“It was one of those days that I could have played against anybody I played so well. But it was nice to get off with a win the first day,” Na said.
“It's not over until it's over. Last year I won the first two matches, halved the third, and I was the only guy not to advance with two and a half points.
“So, yes, obviously Justin Thomas is a strong seed in our bracket so tomorrow is going to be a big day.”
Chris Wood fell to a 2 and 1 defeat at the hands of Justin Thomas in a see-saw battle in the other Group 6 contest, which saw the American have to regain the lead on three separate occasions before sealing victory.
Lee Westwood, the only European Tour player in Group 3, battled in vein as he lost 3 and 2 to Australia's Marc Leishman.
Defending champion Jason Day will play no more part in the tournament after he withdrew from his Group 3 encounter with Pat Perez to be with his mother, who is due to undergo lung cancer surgery.
In Group 14, Daniel Berger produced the widest-margin victory of day one after he defeated J.B Holmes in a 7 and 5 win, while Phil Mickelson was a 5 and 3 victor over Si Woo Kim.
