Jason Day 'just happy' to finish round, defeats Thongchai Jaidee

— -- AUSTIN, Texas -- Jason Day knew he was good to go on Thursday when he stepped to the first tee at Austin Country Club and launched a 3-wood some 370 yards downwind and onto the green, setting up an eagle in the match he eventually won over Thongchai Jaidee.

But Day, the reigning PGA Championship winner who is expected to be among the top contenders at the Masters in two weeks, admitted he was unsure if he would even continue competing in the WGC-Dell Match Play Championship when he arrived at the course after dealing with back pain that he said stems from a bulging disk.

"These things can pop up out of the blue," said Day, who is coming off a victory on Sunday at the Arnold Palmer Invitational and said there had been no issues until the back nine on Wednesday. "For me it happened yesterday on the 15th tee.

"I was just happy that I could get through the round [Thursday] and play solid golf. I actually drove it and hit a lot of good iron shots and putted good."

Day defeated Jaidee 5 and 3, meaning their match ended on the 15th hole. He will face Paul Casey, who halved his match with Graeme McDowell on Friday. With a tie or a victory, Day will advance to the weekend knockout stage.

After his round on Wednesday, Day said he contemplated withdrawing and returning to his home in Columbus, Ohio, to get an MRI. He decided if he didn't feel good warming up on Thursday, that's what he would do. Day could have conceded his match to Jaidee and still played against Casey on Friday, but decided against that scenario.

"I was so disappointed and so angry last night that I was injured because I have been doing the right things," he said. "I have been doing the right things with my body. These things just pop out of the blue, and you can't do anything about it. It's so frustrating because I am playing really good golf right now. I know that if I can keep playing this way, I can win.

"Once again, I'm just trying to stay focused on the positive side of things, that I have recovered pretty good from it. Try and stay on top of it and be disciplined with the protocols and go from there."

Day, ranked second in the world and winner of six tournaments in the last 14 months, said he has had back issues since he was a teenager and recalled having to withdraw from a few tournaments because of it, including the 2014 BMW Championship. Last year at the Barclays, he missed the pro-am but went on to win the tournament anyway.

Day, 28, was cruising to a 3 and 2 victory over McDowell on Wednesday when trouble started on the 15th hole. He hit a poor drive there, and then grabbed his back after hitting his tee shot at the 16th in a fairway bunker.

Because he led by 3 holes with three to play, Day was able to close out McDowell by making a par on the hole, although he went down to his knee while watching McDowell attempt to extend the match.

In brief remarks before getting treatment, Day described it as "searing" pain on both sides of his lower back. No further update was given before Day teed off Thursday.

"The biggest hurdle for me was to get through the warm-up without going, should I push it or should I not," he said. "That was the biggest hurdle for me. Once I got out on the golf course and was focusing on hitting the right shots then I forgot about it, which was good. For me, when I was warming up, at the start it was kind of ginger.

"As I went through, it kind of stayed the same and didn't do anything else. It didn't go down my legs, didn't hurt through impact. I just said, you know what, we're going to go out and play, and it worked out great from there."