SAN DIEGO -- Jason Day worked diligently on his game last week in Palm Springs, looking forward to defending his title at the Farmers Insurance Open, where he won the first of five PGA Tour titles during a breakout 2015 season.
But Day, 28, has been suffering with the flu and wasn't even certain he could tee it up in the first round Thursday at Torrey Pines. He did, and he finished, but he limped home with an even-par 72 after getting to 3-under par early in his round.
"It's mainly just physically, he has no energy," said Col Swatton, Day's longtime caddie.
Day said he felt ill after the round and was unable to speak to reporters.
Day, ranked No. 2 in the world and part of a group of four 20-something golfers who have shot to the top of the world rankings, is playing just his second stroke-play event since the Tour Championship in September. He tied for 10th three weeks ago at the Hyundai Tournament of Champions.
Day birdied three straight holes on the North Course at Torrey Pines early in his round, but had difficulty sustaining the momentum, making four bogeys over the last 11 holes to finish six strokes back of leaders Scott Brown and Andrew Loupe.
"We talked about whether he would even play for the last couple of days," Swatton said. "He wants to compete and play and he's the defending champion.
"Nobody wants to pull out of any event, especially one they are defending. He's really been working on his game, and it's disappointing to come here and not be able to use all that hard work to his advantage."
Day is scheduled to tee off on Friday on the South course at 1:20 p.m. ET.