FARMINGDALE, N.Y. - Usually, when Phil Mickelson tees off in any tournament on the PGA Tour, Amy Mickelson is there to join in the applause and walk all 18 holes, providing love and encouragement.

Today, however, Amy Mickelson will be missing from behind the ropes when the throaty New York throng with its deafening applause welcomes her husband to the 10th tee for his start at the U.S. Open, on the Black course of Bethpage State Park.

The breast cancer of Amy Mickelson, a mother of three and the leader of her husband's support network, was diagnosed last month. Her treatment will begin July 1 and her husband will be with her, having said yesterday that the Open would be his last event "for a little while."

While Mickelson's thoughts won't be far from his wife, who will be watching 3,000 miles away at the couple's home in Rancho Santa Fe, Calif., he is excited about being able to play knowing there have been "little tidbits of good news here and there" since the diagnosis.

"The people here have treated me and my family incredibly, and I love coming back and playing here," Mickelson said. "Bethpage is one of my favorite golf courses. To be able to play in this Open, I'm excited that things worked out.

"But I'm more excited I'm able to play because we've had some good news that has not rushed treatment, has given us the time and an opportunity to see some test results and give us better direction on what we should do to not just cure her, but prevent it from coming back in the future."

Mickelson left his home Tuesday night for Long Island after celebrating his 39th birthday with his wife and children, and said his wife was "doing very well."

"You'd never know that she was going through this right now," he said. "When we get started, it will be different. But she's an amazing person. I don't know how to express how lucky I am. . . . It's hard for me to see somebody that is such a good person go through something so difficult."

Mickelson returned to competition last week at the St. Jude Classic in Memphis, not just to scrape rust off his game in time for the Open, but also to thank well-wishers that included players and their wives and caddies, many of whom organized a "Pink Out" at the Colonial late last month in Fort Worth, Texas.

The well-wishers wore pink to support Mickelson's wife and breast cancer research.

Mickelson said he wanted "to be able to show my appreciation . . . on behalf of myself and Amy, to be able to let them know how appreciative we were. It was important to do that last week so that I'm able to focus more on just playing golf this week."

But focus might be a problem. Mickelson established himself as the people's choice in 2002, the last time the Open was contested at Bethpage. The wild cheering for him helped him defeat everyone except Tiger Woods while on the way to one of his record-tying four runner-up finishes at the Open.

The cheering will be even lustier this time, with plenty of fans asking Mickelson about his wife. It's certain to be a distraction, but Mickelson doesn't see just the side where concentration could be difficult.

"Possibly," he said. "Or it could be that that support helps carry me through emotionally when I'm on the course. I'm certainly hoping for that.

"I'm going to just do the best that I can. I feel like my game is ready, but you just never know. I feel like, emotionally, I'm better. But you just never know. So we'll play it by ear day to day."

As he got ready for his 19th U.S. Open, Mickelson said that his game was in good shape and that he had "been hitting the ball better than I have in a long time . . . and possibly ever" despite his 59th-place finish in Memphis.

"I actually got my swing to where we wanted it to be," he said, referring to himself and teacher Butch Harmon. "I'm very optimistic about my ball-striking this week. I think the key for me will be on the greens. I putted these greens very well in '02. If I have a good putting week, I expect to be in contention on Sunday."

Mickelson will miss his wife's presence and occasional ribbing. But he possesses constant reminders from her in his quest for his fourth major title.

"She's left me a number of little notes, texts, cards, hints, that she would like to have a silver trophy in her hospital room," he said. "So I'm going to try to accommodate that."

Contact staff writer Joe Juliano at 215-854-4494 or jjuliano@phillynews.com.