Then came a call from the urologist while he was eating lunch with his girlfriend at the Buick Open, asking that Mayfair return immediately because something didn't look right. Only when he sat in his office and stared at the film did fear set in.
'It was at that point that I got scared, because it was definitely cancer,' Mayfair said.
The good news -- stunning news, the more Mayfair thought about it -- was getting out of his bed Tuesday morning and driving to Medinah Country Club for a practice round at the PGA Championship.
It was only 12 days ago that he had surgery to remove his right testicle, getting the cancer before it had spread. Five days ago was one of the best days of his life, when Dr. Gil Brito in Phoenix told him tests showed it was gone.
'Two weeks ago today, if you would have told me I was going to be here, I would have never believed it,' said Mayfair, who turned 40 on Aug. 6 -- three days after his operation.
Cancer has always been a word that made Mayfair shudder.
A day rarely goes by without him thinking of Heather Farr, the LPGA Tour player who was diagnosed with breast cancer at age 24 and died four years later in the prime of her life.
She was like a sister to Mayfair.
They grew up together in Phoenix, spending their afternoons on the Papago Golf Course, a public course where they pursued greatness. They shared the same coach, Arch Wadkins, and in 1992 at Palm Beach Gardens, Fla., they won the boys' and girls' division at the Junior PGA Championship.
Both turned sterling amateur records into a spot in the big leagues.
Farr's career ended far too soon.
'I remember the day I was in Hartford, Connecticut, when I called home and my instructor, Arch, told me that Heather was diagnosed with breast cancer,' Mayfair said. 'I didn't know much about it, but being around Heather and seeing what she went through and all that, I learned a lot more. It scares me, absolutely. And I miss her. I miss her terribly.'
Mayfair managed a smile when he recalled the time they met.
Not many girls played junior golf in the early 1970s, and it was not unusual for them to be lumped in with the boys. Mayfair was 8 when he played his first junior tournament, and he wound up in the same group with 9-year-old Heather.
Of all the calls and cards of support he received over the last few weeks, nothing meant more to him than learning that Missy Farr Kaye was in the waiting room at the hospital the day of his surgery.
Missy, now an assistant golf coach at Arizona State, is the younger sister of Heather Farr. It was the death of her sister that taught her to get mammograms every year, which ultimately saved her life. Missy was diagnosed at age 30, but doctors caught it early enough that she has been free of cancer the last eight years.
Word that Mayfair was diagnosed with testicular cancer was a jolt.
'It is rather surreal, there's no doubt about it,' Farr Kaye said Tuesday from Arizona. 'I'm just so thankful the prognosis is excellent. Billy is a resilient guy. He's always got a smile on his face. He understands life is short, and you've got to take care of it and enjoy it.'
Also in the waiting room the day of Mayfair's surgery was Phil Mickelson, one of his best friends on tour.
Mickelson flew from San Diego on Aug. 3 to be at the hospital during the surgery. Talking about Mayfair on Tuesday, Mickelson said he was thrilled about Mayfair's prognosis and amazed that modern medicine would allow him to return to golf so quickly.
He never mentioned that he had gone to the hospital to support him.
'Him being there in the waiting room tells me what kind of guy he is,' Mayfair said.
Mayfair still faces tough decisions.
The cancer was encapsulated, but Mayfair said he either must be tested every two or three months to make sure the cancer is gone, or go through two weeks' of radiation and be tested once or twice a year.
'For now, I've got a clean bill of health,' he said.
And he has a new outlook on life.
Mayfair recalls the last conversation he had with the anesthesiologist, a golf fan and Arizona State alum, just like Mayfair.
'He said, 'How do you handle the pressure of playing before all those people on the 16th hole at Phoenix?'' Mayfair said. 'And I said, 'That's nothing. This is real pressure.' That's the last thing I remember before I went to sleep.'
It must have all felt like a dream. In the span of 10 days, he felt the lump while taking a shower, was diagnosed with testicular cancer, flew home to Arizona, had surgery and received the best news that the cancer was gone.
'I should be thankful just for being here,' he said. 'And I am.'
If the last two weeks felt like a whirlwind, consider the last two years.
Mayfair's game was in such bad shape that he had to take a one-time exemption from the career money list to keep his card for the 2005 season, and he responded by qualifying for the Tour Championship. Once his golf game recovered, his marriage broke up, a divorce that is in the final stages.
And now the cancer.
'Everything happened all at once. Definitely, this has been the hardest year of life-changing things,' Mayfair said.
Then he smiled, happy to be healthy, excited to be at the final major the year without a trace of cancer in his body.
'And you know, if I play four good rounds, it could change my life again.'