Jason Day plays at Austin Country Club.
Jason Day won the battle, but time will tell if he loses the war.
Day played some occasionally brilliant golf to beat Graeme McDowell 3&2 in the opening match of the WGC World Match Play Championship in Texas.
But with the Masters just two weeks away, Day suffered a painful back injury while hitting a driver on the 15th hole.
The Queenslander battled hard for the next 15 minutes and shook hands when McDowell missed a chance to extend the match on the 16th green.
He quickly left the course for treatment, with manager Bud Martin later issuing a statement saying Day was hopeful of playing on at the Austin Country Club.
“Jason tweaked his back on hole No.15 and had some work done post-round,” Martin confirmed.
“He is pleased with the outcome of the match and is getting prepared to play tomorrow.”
Earlier, the world No.2 told AAP correspondent Ben Everill he was “really struggling” before he left the course in obvious discomfort and battling to walk properly.
"It's really hard to play with searing pain in both sides of your lower back," Day told AAP.
“Just my back has seized up and I need to get inside right away for treatment and see what's wrong.”
His second match against Thongchai Jaidee isn't scheduled until later tomorrow.
With the Masters just two weeks away, the injury couldn't come at a worse time for the 28-year-old, who has battled injury and illness throughout his career.
Day came back from two down after the first four holes to win his match against the former US Open champion from Northern Ireland.
He made birdies on the 5th, 6th, 8th, 9th and 12th holes to re-establish a lead, then hung on with pars after that run established a 3-up lead.
Marc Leishman blew a golden chance to take out Ryan Moore when the Victorian couldn’t scramble a par on the closing hole and the American’s four proved enough for a halved match.
Matt Jones led early against Louis Oosthuizen, but the South African made some key birdies on the second nine and eventually held sway 2&1.
Marcus Fraser didn’t play badly against Zach Johnson, but the reigning Open champion was six under when they shook hands on the 15th green with the Aussie suffering a 4&3 loss.
World No.6 Adam Scott was kicking himself after blowing a 2-up lead with three to play in halving his match with Thomas Pieters. The Queenslander led from the sixth hole to the 17th green and looked in command until the Belgian fired two late birdies he couldn't match.