Phil Mickelson escaped the chill embrace of a "snowman" in the desert and, with birdies on two of the last three holes yesterday, became only the second amateur since 1954 to win a PGA Tour event, taking the Tucson Open by a shot.

In golfers' parlance, a "snowman" is a score of 8 on a hole. And it was that ugly number Mickelson logged after hitting two shots into the Arizona-Sonora Desert and one into a bunker on the 14th hole. It was a triple bogey and from a one-stroke lead when he stepped on the tee, he went to three behind and a tie for fifth when he left the green.

"I never thought I'd see anyone come back from something like that," said Corey Pavin, who played with Mickelson in the final group at the TPC at Starpass.

But the 20-year-old left-hander took advantage of a massive collapse by veteran pros and became the first amateur since 1985, when Scott Verplank won the Western Open, to claim a victory on the tour.

Mickelson, a junior at Arizona State who already boasts U.S. Amateur and NCAA titles, scored this triumph over adversity with a closing 71 and a 272 total, 16 under par.

His debacle from sand and scrub on the 14th appeared to leave the struggle to Tom Purtzer, a veteran in his 17th tour season, and 1986 PGA champion Bob Tway.

But Purtzer, playing well in front of Mickelson, blew the lead when he chunked his approach into the front bunker on the 18th hole, failed to get it out and took a double bogey.

Moments later, Tway, playing the 17th, missed the green and failed on a 10-foot par-saving putt.

That dropped each of them back to 15 under par, tied for the lead and one in front of the amateur.

A composed Mickelson responded by lofting his approach within a foot of the flag on 16. The birdie put him back into a share of the lead. He made a routine par on 17.

At 18 he hit his second shot to about eight feet left of the pin. He made the winning putt, hugged his coach-caddy Steve Loy and strolled into the howling gallery.

"I went from having the biggest knot in my stomach to the greatest joy in a half hour," Mickelson said.

"He's a special kid," said Purtzer, who had a closing 67 and tied Tway (68) for second at 273. "He's a kid you'd like to have as a son or brother. I just want them to make sure he stays in school for two more years."

And that's his plan. Mickelson said he intends to complete his degree in psychology in the spring of 1992 before joining the pro ranks.

"Money is not a problem," said the San Diego native, who as an amateur eschewed $180,000 first prize here. "I'm on a scholarship and my folks help me."

When he does turn pro, he will have a 1 1/2-year exemption on the PGA Tour, a pass through the Tour Qualifying School. As for the Tucson payoff, Tway and Purtzer split the first- and second-place purses, each pocketing $144,000.

Palm Meadows Cup: Greg Turner of New Zealand shot 4-under-par 68 for a 271 total, beat Greg Norman by four shots and won the $172,000 top prize in Palm Meadows, Australia.