Debutant Hideto Tanihara showed no signs of stage fright as he produced the shock result of day one at the WGC - Dell Technologies Match Play with a 4 and 2 win over two-time Major Championship winner Jordan Spieth at Austin Country Club.
Tanihara, who only made two birdies in his 16 holes, took advantage of a below-par display from Spieth to improve his chances of playing at the weekend in what is his first time at this event.
After opening the first six holes with pars, Tanihara nailed the only birdie on the front nine from either player when he sank a 16-foot putt on the seventh which the American could not match.
At the turn, the Japanese player landed his approach to within two feet for a tap-in birdie with Speith failing to chip in for a half before Tanihara extended his lead to three up with par on the 12th when the World Number Six found water with his second shot.
Spieth hit back to reduce the scores to two up after 14 when Tanihara's tee shot found the water but 38 year old responded immediately with a birdie on the next to set up dormie three, which the American conceded after ditching his fourth stroke into the greenside bunker.
Tanihara was delighted to start with a victory, he said: "Today was an enjoyable day. I was look forward to playing. I knew if I brought my "A" game, I could probably compete against him.
"Trying to win the whole tournament, you have to go through tough guys. So (I am) just happy to get this win."
In the other Group 5 match, Ryan Moore and Yuta Ikeda ended all square.
Charl Schwartzel put himself in the driving seat heading into day two after a comfortable 6 and 5 win against Byeong-hun An.
The two players traded the opening two holes before An went one up at the fourth but the 11-time European Tour winner made it all square at the fifth when his approach to within five feet handed him his first birdie.
Today was an enjoyable day. I was look forward to playing. I knew if I brought my "A" game, I could probably compete against him - Hideto Tanihara
Schwartzel went one up after the sixth despite finding the bunker as An missed a six-foot putt for a half before pars on holes eight and nine put him three up, with the South African turning the screw with his second birdie of the match on the tenth before sinking successive gains on the 12th and 13th to seal an opening success.
He said after his convincing victory: "It was good stuff. We both played fairly rough in the beginning. We were up and down and then I found my feet.
"I started playing really solid and bringing a lot of pressure. Applying that much pressure, I got it done."
In the other Group 12 clash, Joost Luiten fell to a 2 and 1 defeat to Paul Casey in a see-saw battle.
In Group 4, Louis Oosthuizen eased to a 4 and 3 win over Ross Fisher.
He gained an early initiative on the third after Fisher found water with his drive but the Englishman levelled with a birdie on the fifth.
I started playing really solid and bringing a lot of pressure. Applying that much pressure, I got it done - Charl Schwartzel
Oosthuizen responded at the next with a birdie of his own when he reached the green of 590-yard par five in two to re-establish the lead before picking up gains on the eighth and 11th in addition to a par on the 12th.
Hideki Matsuyama and Jim Furyk finished all square in their Group 4 clash.
Thomas Pieters started with a 3 and 2 success over Scott Piercy and took an early lead when he parred the third to go one up before both players exchanged birdies on the next two holes as the Belgian remained ahead.
Pars on the 11th and 12th were enough to put Pieters three up before the duo traded the next two holes with pars before the World Number 34 secured victory.
Bubba Watson got the better of Jhonattan Vegas with a one up success in the other Group 13 encounter.
