Rory McIlroy is into the last 16 of the WGC-Dell Match Play after defeating Kevin Na on the second play-off hole at Austin Country Club.
The defending champion came into the final day of the group stage facing a winner-takes-all clash against Na in Group 3 and the two men could not be separated after 18 holes.
They both made par on their return to the first but, after Na was forced to take a drop after putting his tee-shot on the second into the trees, a par was enough to see McIlroy progress.
"It was tough," he said. "All three of my matches this week have been pretty tough.
"I didn't get off to a best of starts again. Found my rhythm in the middle of the round, started to make some birdies and hit some good shots when I needed to.
I feel like my game has gotten a little bit better as the day's gone on. I know I will have to play very well again tomorrow to try and beat Zach - Rory McIlroy
Bunker trouble resulted in a double-bogey on the second which saw McIlroy go one down and a Na birdie on the fifth doubled his advantage. But the World Number Three put his tee shot on the seventh to eight feet and when he rolled in a 68-footer on the ninth, they were level at the turn.
The duo then traded birdies on the tenth and 11th before a birdie on the 15th moved McIlroy ahead. The Northern Irishman then found the water on the 16th and despite nearly holing his chip for a par, Na got back level and both men parred their way home.
In the dead rubber in Group 3, Thorbjørn Olesen beat Smylie Kaufman 2 and 1.
McIlroy will face Open Championship winner Zach Johnson next after the American maintained his 100 per cent record in Group 14 with a 4 and 3 win over Shane Lowry.
Martin Kaymer was also a 4 and 3 winner against Marcus Fraser.
Branden Grace was defeated in a play-off as Chris Kirk advanced from Group 11.
The South African beat Russell Knox 5 and 4 in his final group match to set up the play-off with Kirk, a 3 and 2 winner over David Lingmerth.
Grace found sand off the tee on the first play-off hole and when he put his third over the green, he had to settle for a bogey as Kirk made par.
Bill Haas beat Adam Scott by one hole and will face Kirk next, while Thomas Pieters was a 3 and 2 winner over Chris Wood in the other Group 6 match.
Danny Willett and Jaco Van Zyl both recorded victories in Group 10.
Willett completed a 4 and 3 victory over Brooks Koepka, who still won the group thanks to Van Zyl's 2 and 1 win over Billy Horschel.
Matt Kuchar is next up for Koepka after he beat Justin Rose 3 and 2 to win Group 7, where Anirban Lahiri was a 4 and 2 victor over Fabian Gomez.
Jason Day advanced from Group 2 after Paul Casey withdrew from their match due to illness and will next face Brandt Snedeker.
Snedeker was a 5 and 3 winner over Charl Schwartzel, with Charley Hoffman claiming a 4 and 2 win over Danny Lee in the other Group 15 match.
Thongchai Jaidee and Graeme McDowell halved their Group 2 match.