Paul Casey conceded his opening game of the WGC-Dell Technologies Match Play due to back spasms after completing just two holes.
Casey won the opening hole with a par against group 10 opponent Corey Conners, but lost the second when the Canadian holed out from 148 yards for an eagle.
The pair had hit their tee shots on the par-four third hole when Casey signalled he was unable to continue.
The 44-year-old, twice a runner-up in this event, has not conceded his remaining group matches against Alex Noren on Thursday and Louis Oosthuizen on Friday and could still win both to potentially advance to the last 16.
The 64 players at Austin Country Club are split into 16 groups of four with only the pool winners advancing to the knockout stages at the weekend.
Group 11 features four major champions in the shape of Jordan Spieth, Adam Scott, Justin Rose and Keegan Bradley, with Spieth beating Bradley 2up and Scott defeating Rose by the same margin.
Rose made a remarkable par on the 17th to keep the match alive, holing out from 98 yards from the drop zone after pulling his tee shot into the ravine to the left of the green, only to bogey the 18th.
The first full result of the day had come in group 14 as Maverick McNealy, who was the last man into the event on Monday when Sam Burns withdrew, made the most of his late call-up with an 8 and 6 thrashing of Joaquin Niemann.
“I was home last week, really hoping I’d get the chance to play, preparing like I was going to get a chance to play and had a nice round today for sure,” McNealy said.
“He’s a great player and he’s the type of guy that can rattle off five birdies in a row at any given time, so I knew I had to keep the pedal down and hopefully run out of holes before that happened.”
The largest margin of victory in the event was achieved by Tiger Woods in 2006, who beat Stephen Ames 9 and 8. Ames had questioned Woods’ performance off the tee before the match, saying that “anything can happen, especially where he’s hitting the ball”.
