SAN FRANCISCO • World No. 1 Jordan Spieth and third-ranked Jason Day are battling just as hard to avoid being changed by success as they are to win this week's PGA Pebble Beach Pro-Am.

The 20-something stars, who each won breakthrough Major titles last year, top the golfing talent at the annual match-up of celebrities and elite players over three courses along the United States' Pacific coast.

Spieth, the reigning Masters and US Open champion, has not seen much change since ascending to the top ranking.

"When that label is said, I think if you're in the top five or top 10, it's the same impact," said the American, who finished second at the Singapore Open in his last start and is feeling refreshed after a week-long break. "When you're at the top, there's a bit of a difference. There's just more of an interest.

"I don't think I have to go out of my way to change who I am or what I'm doing. A label shouldn't change who you are - good or bad."

Australia's Day, who won his first Major title at last year's PGA Championship, revels in his sameness.

"Life has not changed for me. I'm still the same boring person I was before I won a Major," he said ahead of yesterday's first round. "I'm fine with that."

But the revelation he expected after winning a Major and reaching world No. 1 never came, or at least not in the way he expected it would when he woke up the next morning and felt unchanged.

"I always thought there would be this moment, this sense of clarity - I've done all I needed to do," he added. "Unfortunately, it never really happened. That just told me I have to go out and do it more."

Day has children to consider when planning his schedule and practice routine, which is not a factor for his other rivals among the world's young top four stars - Spieth, second-ranked Rory McIlroy and fourth-rated Rickie Fowler.

"Rickie, Rory and Jordan don't have kids," he said. "And it's important for me to be there and see them grow up. They will probably be there one day and have the same things I do. Keeping that balance as a professional golfer is difficult."

Those who carry the golfers' bags have other challenges.

A lawsuit filed by a group of caddies against the United States PGA Tour for alleged mistreatment has been thrown out by a US District Court judge.

A group that grew to 168 caddies filed the lawsuit last February, claiming they are walking billboards - forced to wear bibs with sponsor logos without any proceeds from sponsor contracts that were estimated at US$50 million (S$69 million) a year.

But, in a Tuesday ruling, according to the network, judge Vince Chhabria found "the caddies' overall complaint about poor treatment by the Tour has merit but this federal lawsuit about bibs does not".

"Caddies have been required to wear the bibs for decades, so caddies know when they enter the profession that wearing a bib during tournaments is part of the job," Chhabria wrote. "For that reason, there is no merit to the caddies' contention that contracts somehow prevent the Tour from requiring them to wear bibs."

He also tossed out the caddies' claims of anti-trust and trademark violations and the notion their contracts with the Tour were signed under duress. The PGA Tour said it was happy with the ruling.

"We are aware of the ruling made in our favour regarding the lawsuit filed last year by caddies and are pleased by the court's decision," its statement said. "We look forward to putting this matter behind us and moving forward in a positive direction with the caddies."

AGENCE FRANCE-PRESSE