Australian Day turns back the clock at PGA Championship

SAN FRANCISCO (Reuters) - Jason Day has battled a chronically bad back for years but on Thursday the former world number one looked like a younger and healthier version of himself as he grabbed the first-round clubhouse lead at the PGA Championship.

Day arrived at TPC Harding Park in chilly San Francisco fresh off top-10 finishes in each of his three previous starts but this week had to deal with temperatures that are not ideal for those with back issues.

The 32-year-old Australian, who finished in a share of sixth place at last week's World Golf Championships event in Memphis, said his back felt fine in Thursday's opening round but that the colder conditions do make him cautious.

"You got to be careful," said Day. "It was nice to play in the hot weather last week and coming to this week you are always cautious doing certain things - bending over.

"But I pretty much lather up in deep heat (ointment) and go out. I try to burn the skin off my back to be honest. I feel pretty good."

Day, whose only major win came at the 2015 PGA Championship during a stretch when there was arguably no better golfer on the planet, enjoyed a bogey-free trip around TPC Harding Park where he carded a five-under-par 65.

A 12-times winner on the PGA Tour, Day began his day on the back nine and got to work early as he made a nice up-and-down from 46 feet at the par-five 10th for an opening birdie.

"Today I drove it really nicely, and when I was out of position, I left myself on the right side of the fairways to be able to at least get somewhere around the greens, and if I did miss the greens I left it in the right spot," said Day.

"Pretty sound the whole way around."

While Day's back has allowed him to produce solid results of late, he also credits his recent form to being mentally tougher and no longer struggles to get up and play but rather looks forward to competing each week.

"I finally had enough of feeling sorry for myself, and it's easy to do that in this game because it is so mentally tough," said Day.

"You can start blaming everything else but yourself. Sometimes you've just got to pull your pants up and just move on, you know."

(Reporting by Rory Carroll; Writing by Frank Pingue; Editing by Stephen Coates)