Every game has levels of performance, but no sport has the exhilarating or terrifying mobility of pro golf. From great to awful, you seldom know quite where you stand in this constantly shifting world. Everywhere here at the U.S. Open we see players in the midst of stunning changes, few of them connected to injury or age, but rather to mysteries unique to golf.

Consider Phil Mickelson. Six months ago, he was supposedly a legendary choker, his reputation nailed down by a dozen years of consistent disappointment, including 46 consecutive majors without a victory. Now, in half a season, with the right attitude adjustment, better physical conditioning and a new receptivity to proper coaching, Lefty finds himself the owner of a Masters green jacket and is now tied for the Open lead after two rounds.

In two days, far-fetched as it would have seemed at the end of last season, we could be talking about Mickelson having a chance for a "real" Grand Slam -- all four major championships in the same calendar year -- as opposed to the Tiger Slam.

Did someone mention the great Woods? Here he's been in the rough, in the sand, in a funk. His slump is now deep into its second season. Will Woods awake one day and find himself at a new and lower level of the game? How long can you perform like a lesser player before you, in fact, become that new fellow? Such a day hasn't arrived for Tiger and may never. Even Jack Nicklaus had fairly long lulls until he got disgusted enough with himself to revamp his swing or rediscovered his motivation.

Nevertheless, every step Mickelson takes here reminds us of the Woods walk that was once so familiar. Mickelson has looked like a stalking lion on the links of Shinnecock Hills. With his determined pace, bent forward with shoulders rolling as he comes up the fairway, he looks like the quintessential man on a quest.

Whatever lies ahead, Mickelson can't wait to get there. From tee to green he's cheered here, his name yelled everywhere and always with praise. Whatever happened to Pholdin' Phil? He's gone, changed, almost evaporated. You couldn't bring him back if you tried. A new man, similar but deeply different, stands in his place.

"What I have is a sense of excitement and anticipation. I can't wait for the upcoming majors now because I feel like I'm onto something," Mickelson said after shooting a bogey-free, second-round 66 that was strategically sound and thrill-free. "It's only been five or six months since I've figured out how to prepare properly for majors. If I keep working on the right things, where will I be in 12 or 18 months?"

In golf, 12 to 18 months can be enough time for an eternity of improvement or of disintegration. Careers are born or reborn, misplaced or squandered in that time frame. Just 18 months ago, 50-year-old Jay Haas was considered a golf relic. Now, he's dreaming of true greatness for the first time in his life. Can he win a major title this year or next? Why not? Will he dominate the Champions Tour with its beckoning millions? Bet on it. That now looks like a lock.

The mirror image of Haas is 32-year-old David Duval, who was No. 1 in the world just five years ago. However, he burned with such obsessive intensity that, one week after winning the 2001 British Open, he began losing his appetite for the game. "Is that all there is?" he says he thought. While Haas's face beams when he mentions what he might accomplish in "the next 10 years," Duval won't even say when, or if, he'll play again. "Whenever I feel like it again," Duval said, after shooting 83-82 here.

After watching Duval, who was in the top 10 on the money list just three years ago, the same question crosses many minds. Though he has no serious injuries, will he ever make another cut? That is to say, ever earn another dollar in his chosen profession? In the '90s, former British Open champion Ian Baker-Finch reached this same impasse. Nothing was wrong with him, except that he could no longer play world-class golf. The gift disappeared. Duval claims he's at the beginning of some semblance of a comeback. But Baker-Finch thought the same. Golf disagreed. He never cashed another check.

Is it really proper to describe such an activity as a "game?"

The precariousness of golf, both technically and psychologically, cannot be overstated when compared with other sports. Every game has the occasional pitcher who loses his control or the quarterback who misplaces some confidence. But, barring injury, complete collapse is rare. Not in golf. That's why fear is often the sport's best motivator. It certainly was for Mickelson.

Last season, he saw his game, his status, and his career as a premier player, slipping away. Falling to 38th on the money list sacred him to death. Mickelson quit his famous passion for gambling both on the course and off. He worked out and lost weight. Phlabby Phil disappeared, too. Finally, he listened to two excellent coaches -- Rick Smith for his swing and pre-tournament preparation and Dave Pelz for the short-game and course strategy.

"Having a year as rough as last year forced me to sit down, reevaluate things and change things," said Mickelson on Friday. "Had I gone along having so many close opportunities [in majors] and not capitalizing [on them], I may have continued without making the necessary changes."

So, Smith taught him a power fade. Now, Mickelson, who has sacrificed some distance for accuracy, shapes every tee shot here, either draw or fade, so he can hit more fairways. Smith and Pelz now spend several practice rounds with Mickelson before each major championship. What Nicklaus always did -- come early, play more practice rounds than anybody and work on specific shots for particular holes -- Mickelson now deems wise as well.

At 34, Mickelson has frittered away a dozen chances at majors. But he may yet have a dozen more opportunities. Told yesterday that his play here has been almost boring, Mickelson smiled with pride. "Yes," he said. "But the outcome is okay."

With that, our older and finally wiser Mickelson departed so that he could perform one last act of ritual preparation, though some might call it penance for all the short clutch putts he's blown over the years. The master of the foolhardy Tin Cup gamble, the pro most likely to try a 280-yard 3-wood shot out of deep rough over an alligator swamp, was off to work on his latest daily routine. Make 100 three-foot putts in a row.

"So far," said Mickelson, "I've done it three times this week."