Ian Poulter is through to the last 16 of the WGC - Dell Technologies Match Play after Kevin Chappell conceded their Group 9 match on Friday.
Match play specialist Poulter was three up after eight holes when his American opponent informed him he would not be able to continue.
The victory keeps Poulter's 100 per cent record intact and sets up an encounter with Louis Oosthuizen after he came through a play-off against Jason Dufner.
It was a strange ending to a match. I've never had that happen before - Ian Poulter
Poulter said: "I warmed up with him in the trailer this morning and didn't know anything was wrong, but obviously something wasn't quite right.
"I chipped it down to a couple of feet on the ninth, was going to tap that in to be three-up going to the tenth and he comes over and says 'Ian, I can't go anymore holes, my back is not right'.
"So hopefully he gets better soon. It was a strange ending to a match. I've never had that happen before.
"Hopefully I can conserve some energy and have a strong weekend."
Race to Dubai champion Tommy Fleetwood beat Daniel Berger 2 and 1 in Group 9's other game, but with Chappell conceding early, a place in the last 16 was out of reach before he even got to the turn.
Oosthuizen beat Jason Day by two holes on Friday to claim his second point but with Dufner seeing off James Hahn 3 and 2 in Group 8's other match, a play-off was required to decide who progressed.
The South African then calmly slotted in his par putt from around 12 feet at the first extra hole to book his place in the next round.
Oosthuizen knows he faces a tough test against Ryder Cup stalwart Poulter.
He said: "It will be tough. It's definitely going to be tough. I'm looking forward to it.
"Anyone on a good day can take it all.
"Yeah, it should be good fun. He's obviously got a good track record and he's playing well."
Matt Kuchar advanced from Group 16 after cruising to a 6 and 4 win against Ross Fisher which will be remembered for his stunning hole-in-one at the seventh.
Kuchar won three of the first five holes to establish a commanding lead only for Fisher to reduce the deficit with an eagle at the fifth.
But the 39 year old American holed his tee-shot with an eight-iron at the 181-yard seventh to restore his three-hole advantage and he never looked back.
Kuchar then won the ninth, tenth and 11th to go six clear with seven holes remaining.
He was thrilled to get an ace. He said: "Any time you get a hole-in-one, it's awfully special, awfully fun.
"In this format it's cool. There's kind of two sides to it in this format. It guarantees you a win, most likely.
"And on the other side, it may just win you a hole by one, one-up.
"I think in typical stroke play, getting a hole-in-one, you figure you gain two shots on the field and you are up a little more than normal."
Fisher fired another eagle at the 12th to keep his hopes alive but Kuchar won the 14th to wrap up a straightforward win.
Zach Johnson's clash with Yuta Ikeda finished all square in the other game in the group.
Kuchar will come up against Kevin Kisner on Saturday after he beat World Number One Dustin Johnson 4 and 3 to finish top of Group 1.
Adam Hadwin looked set to force a play-off after notching a birdie at the 17th to go one up against Bernd Wiesberger in the group's other match but the Austrian won the 18th with a super 15-foot birdie putt to halve the match.
