Louis Oosthuizen made the last eight for the third season running after beating World Number One Jordan Spieth 4 and 2 in their round of 16 match at the WGC-Dell Match Play.
With both men going into the last 16 with 100 per cent records in the group stages, the crowd at Austin Country Club were set for an intriguing match-up.
The first three holes were halved but when Spieth hit his tee shot on the par three fourth right, Oosthuizen took advantage and moved ahead with a two-putt par.
Spieth missed the green again on the next par three at the seventh, this time coming up short, and the South African was again on hand to capitalise, putting his tee-shot to six feet for a birdie.
The American played the eighth beautifully, finding the middle of the fairway with his drive and then putting his second to 12 feet for a birdie to close the gap.
But he found a bunker off the tee on the ninth and a par was enough to give Oosthuizen a two hole cushion.
Despite a 26-foot putt on the tenth, Spieth was always playing catch up as Oosthuizen, winner of the ISPS Handa Perth International, capitalised on a double-bogey to claim the next three holes, including a 20-foot putt on the 13th, to stretch his lead to four.
The American hit back with a birdie on the 14th but Oosthuizen sealed the win with his fifth birdie of the match to advance into the quarter-finals.
"I was definitely the underdog," said Oosthuizen. "I just wanted to go out and play solid golf. Jordan played great. We both played great. He put a lot of pressure on me with a few long putts he made early on. I was just trying to give myself as many putts for birdie as I can.
"This morning I think got a bit lucky, not as many people out there early when we teed off. When I got down to 11 and 12, I could see everyone behind Jordan, which I expected.
I played nice, solid golf. I made good birdies at crucial times and if I can do the same this afternoon, I'll have a good shot - Louis Oosthuizen
The South African will play Dustin Johnson in the last eight after the American beat Patrick Reed 3 and 2.
Reed took the lead with a birdie on the par five sixth but a 41-foot putt from Johnson on the seventh levelled matters before bunker trouble off the tee saw Reed drop the ninth.
The World Number Nine saved par on the tenth to square the match but Johnson made three birdies and an eagle in four holes to ensure his passage to the next round.
