Defending champion Rory McIlroy will face a winner-takes-all clash against Kevin Na at the WGC-Dell Match Play on Friday after overcoming Smylie Kaufman in his second Group 3 match.
The World Number Three beat Kaufman 3 and 1 to make it two wins from two but he has been made to battle for both his victories and, in terms of tournament seeding, faces his toughest test of the week so far against Na.
The American defeated Thorbjørn Olesen 3 and 2 to also maintain his 100 per cent record and end the Dane's campaign at Austin Country Club.
McIlroy birdied the second to go one up but then found a bunker on the third and pulled his tee shot on the fourth to slip behind. Back-to-back birdies on the fifth and sixth turned the match on its head again but Kaufman hit back on the tenth to level things up.
The American then moved ahead as McIlroy had to concede after finding the water off the tee on the 11th but Kaufman returned the favour on the 13th and 14th to give McIlroy the edge.
A birdie on the 15th extended the lead to two holes and another wayward tee-shot on the 17th ended Kaufman's hopes.
Knowing that I'm playing Kevin, and you win or you're heading home, probably be a little bit more intensity tomorrow - Rory McIlroy
"I feel like I've played well for the most part. I got through yesterday, which was the most important thing but felt like the quality of my game today went up a level which was nice to see.
"Hopefully I can continue to do that as the week goes on."
Branden Grace's future is in his own hands after he claimed a 4 and 3 win over David Lingmerth in Group 11.
The South African made a birdie-birdie start and never looked back, also winning the seventh, tenth, 11th and 12th as he never trailed against his Swedish opponent, who is now eliminated.
"I think no bogeys on the scorecard on my behalf was maybe key," said Grace. "I think that was good, especially around this track."
Grace will face Russell Knox on Friday with both men able to advance after the Scot recovered from losing the first two holes to beat Chris Kirk.
The WGC-HSBC Champions winner pulled himself all square on the ninth and then won the next two holes en route to a 2 and 1 victory.
"It's going to be a tough match," said Knox of his clash with Grace. "I'm going to have to play probably better than I did today."
Marcus Fraser and Shane Lowry both saw their chances of making the round of 16 disappear as they halved a wild contest in Group 14.
Lowry was three up at the turn but when Fraser birdied the 17th, the match was turned on its head before the Irishman claimed the last.
Martin Kaymer was beaten 8 and 6 by Zach Johnson and needs the American to lose against Lowry on Friday if he is to have a chance of progressing.
Thomas Pieters and Chris Wood both made early exits in Group 6 as they suffered defeats in their second matches on Thursday.
The Belgian was beaten 4 and 2 by Bill Haas while Wood went down 3 and 2 to WGC-Cadillac Championship winner Adam Scott.
