FARMINGDALE, New York – Phil Mickelson postponed his planned arrival Tuesday at the US Open to spend his 39th birthday with wife Amy as she fights breast cancer, but both were in the thoughts of his main rivals.

Mickelson will arrive Wednesday and tee off Thursday in the first round of the 109th US Open trying to win a title after four prior runner-up finishes while fighting back the heartache and uncertainty of his wife's condition.

"I can only imagine how difficult it's going to be for Phil," said England's Paul Casey, who played a practice round with Mickelson last week. "I could just look in his eyes and you can see that he's not his usual self."

Amy Mickelson was diagnosed with cancer a month ago, prompting the world's number two golfer to leave the tour to be with her. Doctors delayed treatment until July, saying they appeared to have caught the cancer in its early stages.

"She's a sweetheart. She's so nice and generous to everyone she meets," said world number one Tiger Woods. "Everyone out here hopes that she gets well and she gets back out here as soon as she can."

Before treatment, Mickelson will take his wife on a tropical vacation. This week he tries to claim an elusive crown at Bethpage Black, where spectators cheered him on like never before in 2002 when he finished second to Woods.

"He's loved up here and he would love to win the US Open at Bethpage," Casey said. "I hope he does play great golf and if I can't win, I think it would be very fitting or great that Phil would win."

Three-time major champion Mickelson shared 59th last week at Memphis in a tuneup event to prepare for the emotional and golfing challenge awaiting him this week, a gauntlet that daunts even 14-time major champion Woods.

"I couldn't imagine dealing with what he has to deal with on a daily basis. And hats off to how he's handled it because certainly it's so hard to do," Woods said. "I don't know how they're doing it. But certainly it's difficult."

Woods, who played while his late father Earl was very ill, knows even well-meaning supporters can remove what little sanctuary the golf course provides.

"Everywhere you go people are reminding you of it and you can't get away from it," Woods said. "You think the golf course would be your escape, but it's not.

"You're surrounded by people wishing you well the entire time and hope everything works out. But then again, they keep reminding you of the same circumstance you're dealing with on a daily basis."

At the same time, the cheers can rejuvenate a flagging spirit.

"You try to find energy from somewhere," Woods said. "You don't sleep much. It's hard. To find energy from outside the ropes, sometimes that's a great thing."

Northern Ireland's Darren Clarke, who lost his wife Heather to breast cancer in 2006, offered Mickelson some comfort and solace.

"We had a good conversation about various things," Clarke said. "He's a good friend. It's very sad news but it's early stages so we all hope the tests and everything else go as well as we wish."

Ireland's Padraig Harrington, who won last year's British Open and PGA Championship, said the challenges of pondering club choices, putt breaks and wind influences are something golfers can fall back upon.

"Any time a golfer is going through something in his personal life, that's unfamiliar territory," Harrington said. "When Phil is on the course that's probably the easiest place for him to be because he's good at that part.

"I would assume it will be better on the course and the crowds will help."

US veteran Kenny Perry, the Masters runner-up in April, has a sister who has fought breast cancer for 18 months and a mother with cancer. He marvels that Mickelson can even be here at all.

"If it was my wife, I don't know how I could sit there and concentrate and play golf to tell you the truth. My mind, my focus would be somewhere else, especially if I was in Phil's shoes," Perry said.

"Here is a guy he doesn't need to prove anything to anybody. He's one of the best we've got out here on tour and Amy is such a sweetheart too. She's a fighter. I know she's tough and I think they are going to be just fine."