Louis Oosthuizen claimed his second consecutive group stage win after beating Bernd Wiesberger 2 and 1 at the WGC-Dell Match Play on Thursday.
The South African, who has reached the quarter-final stage in the last two WGC-Match Play Championships, holed a 12-foot putt to go one up after six holes at Austin Country Club.
Wiesberger would birdie the next hole but two bogeys on the ninth and tenth saw the three-time European Tour winner trail by two before Oosthuizen clinched the win on the 17th.
Andy Sullivan came out on top in his back-and-forth clash against Australia's Matt Jones, claiming a 2 and 1 victory in the other match in Group 16.
I felt like I could do some damage this year - Andy Sullivan
"I know I struggled last week but I feel back to normal this week and I feel I can go quite a long way in the tournament."
European Tour Members Oosthuizen and Sullivan will now face off in a winner-takes-all clash on Friday to determine who advances into the round of 16.
World Number One Jordan Spieth made it two wins from two in Group 1 after beating Victor Dubuisson 5 and 4.
Both men earned wins on day one but the American, who is looking to build momentum ahead of defending his Masters Tournament title, was three up after seven holes with birdies on the third and fifth.
A 23-foot par saver from Dubuisson on the 11th trimmed the deficit to two but wayward tee shots on the next two holes saw the 2014 runner-up fall behind by four and slip to defeat.
Jamie Donaldson beat Justin Thomas by two holes in a nip-and-tuck battle to keep his qualification hopes alive.
The Welshman led by one after seven holes but Thomas bounced back, saving par before making a birdie on ninth to grab the lead. A 19-foot birdie on the 14th helped Donaldson regain the lead and he went on secure his first group stage win.
Phil Mickelson and Patrick Reed will battle for the top spot in Group 9 on Friday after both men were winners on day two.
Reed made three birdies en route to beating Matthew Fitzpatrick 4 and 3, ending the Englishman's hopes for qualification, while Mickelson edged past countryman Daniel Berger with a one hole victory after their match was all square through 17 holes.
"It feels a lot better this year going into our final match in our group play, basically in my own hands. If I go and play some good golf, take care of myself, I move on," said Reed.
Thailand's Kiradech Aphibarnrat could not repeat his day one heroics as he was beaten 5 and 4 by Dustin Johnson in Group 8.
Johnson, who suffered a shock defeat to 49th seed Robert Streb on the first day, responded well as he led by four through ten holes after a 36-foot putt before sealing the win.
A birdie-birdie run on the fifth and sixth before holing a 12-footer on the 11th saw Jimmy Walker beat 22nd seed beat Streb 4 and 3 to leave it all to play for on Friday.
