Charl Schwartzel continued his strong recent form as he beat Charley Hoffman 3 and 2 at the WGC Dell-Match Play at Austin Country Club.
The 31 year old has already won the Alfred Dunhill Championship and the Tshwane Open on home soil this season and battled his way to a gutsy win over Danny Lee in his first match.
A birdie on the third gave the South African a two-hole lead but it was not all plain sailing for the 19th seed as Hoffman claimed the fourth and fifth to square the match.
Schwartzel eventually edged in front with a 16-foot birdie putt on the 13th before seeing out victory.
The 2011 Masters Tournament champion will face Group 15 rival Brandt Snedeker for a place in the round of 16 as the 15th seed halved his match against Lee.
Jason Day quashed any concerns about his back problem as he emerged victorious over Thongchai Jaidee.
The World Number Two was a doubt to play on day two after appearing to injure his back in the latter stages of his 3 and 2 win over Graeme McDowell on Wednesday but a 372-yard drive on the opening hole set up an eagle.
Birdies on the fifth and eighth saw Jaidee trail by one before a brilliant approach allowed Day to make a birdie on the ninth as the Australian went on to seal a 5 and 3 win.
Graeme McDowell and Paul Casey halved their match with the result ending both men's chances of advancing from Group 2.
The Northern Irishman maintained a two-hole lead until a birdie from Casey on the 15th set up a tense finish.
Casey would then square the match on the 17th but neither man could claim the all-important final hole as both saved par.
The Race to Dubai leader Danny Willett was beaten 3 and 2 by 40th seed Billy Horschel, ending his hopes of qualifying for the round of 16.
The Omega Dubai Desert Classic champion needed a win to have a chance of advancing and the Englishman made a birdie on the fourth to get off to a good start.
But the American responded with a birdie on the next hole to level the contest. A bogey on the 14th saw Willett trail by two holes as Horschel birdied the 16th to set up a crucial Group 10 clash against Brooks Koepka on Friday.
Koepka led from start to finish as he claimed a 5 and 4 victory over Jaco Van Zyl.
Anirban Lahiri missed the chance to claim a much-needed win as he halved his match with Justin Rose.
Lahiri, who suffered a heavy defeat to Matt Kuchar on day one, led by one hole after escaping the greenside bunker on the fourth hole to save par.
The 2015 Hero Indian Open champion continued his good play as he drained an eagle on the 16th but a wayward tee shot on the 17th meant Lahiri gave Rose the chance to salvage a half.
The half point for me there is huge because it gives the opportunity tomorrow where I know what I have to do - Justin Rose
"I know if I beat Kuch (Kuchar) tomorrow, I go through. Whereas if you are 1-1 going into tomorrow, there's so many scenarios. So that was a big half point for me."
Kuchar and Fabian Gomez halved their match with Rose facing off against the former in a Group 7 decider on Friday.