Greg Norman had more raw talent than anyone during the height of his powers. He spent nearly three years at No. 1 under Harmon's watch, including a second British Open title and a victory in THE PLAYERS Championship with a score (24 under) that might never be broken.
The other guy Harmon helped take to the top was Tiger Woods, a relationship that lasted nearly 10 years and included four consecutive majors, three straight U.S. Amateur titles, the career Grand Slam and an overhaul of his swing in the middle of all that.
Harmon knows what he's doing. Even some of his fiercest rivals in golf instruction concede that.
But his next project - another bundle of ability - is the tallest order yet.
'Butch, the 1st of many,' Phil Mickelson wrote on the 18th flag after winning THE PLAYERS Championship with precision rarely seen from such a swashbuckler.
Maybe he used '1st' instead of spelling it out because Mickelson was in a hurry. Or perhaps this is the first time Mickelson has reason to believe he can be No. 1 in the world.
Harmon was the center of attention Sunday afternoon as his latest student accepted the crystal trophy for beating the toughest field in golf. They have been working together only a month, and already are seeing results. Harmon put no limits on how much better Mickelson will get as they start preparing for the U.S. Open at Oakmont for now, and taking on Woods in the future.
'You've got to realize you're dealing with one of the most talented people that's ever played the game,' Harmon said.
Woods missed this conversation because he had left the TPC Sawgrass long before Mickelson even teed off. One week after winning the Wachovia Championship against a stellar field on a demanding golf course, Woods couldn't break par until the final round, when four straight birdies and an eagle carried him to a 67 and a tie for 37th.
Even so, Woods remains a bigger obstacle than any flaws Mickelson is trying to correct in his swing.
Harmon has taken two players to No. 1, but he never had to chase down a guy of Woods' stature.
Mathematically, Woods has twice as many points as Mickelson in the world ranking and likely still stay at No. 1 for at least the rest of this year. Mickelson, who can sound like a rocket scientist at times, is aware of this.
'There's such a big lead in the way the points are that it's a two-year process from whenever somebody starts,' Mickelson said when asked if he could get to No. 1. 'But I haven't thought about that yet. I still have a lot of work to get my ball-striking to where I would give myself a chance to contend.'
In the last 10 years, only Norman, Ernie Els, Woods, David Duval and Vijay Singh have been No. 1. Duval got there in 1999 after winning 11 out of 34 starts on the PGA TOUR as Woods was revamping his swing. Singh reached the top in 2004 by winning nine times and a major, while Woods again was rebuilding his swing under Hank Haney.
Paul Casey was asked late last year whether it was an unreasonable goal to aim for No. 1.
'It can be done, and I don't think Tiger would disagree,' Casey said. 'But he would find a way to work twice as hard to make sure it didn't happen. And that's the difficult part.'
No matter what Phil does next, Woods figures to have the final say.
It would be easy to get caught up in one week, one victory at THE PLAYERS Championship. And while Woods looked ordinary at Sawgrass, he still has won nine times in his last 13 starts on the PGA TOUR, including two majors and a runner-up finish at the Masters.
That's where Rory Sabbatini sounded silly last week in saying that Woods struggled with his swing to win the Wachovia Championship, and he looked 'more beatable than ever.'
'I've won three times this year, the same amount he's won in his career,' Woods said, as if flicking a mosquito from his shoulder. Some were quick to say Mickelson would be the favorite at Oakmont, although that could change if Woods wins the Memorial this month.
Even so, Mickelson presents the most tantalizing rival.
He was good enough to win a PGA TOUR event while still in college. He has piled up 31 victories and three majors during his 15 years on tour, numbers surpassed only by Woods among active players. But his discipline has been lacking, either with a swing that went too far past parallel or a strategy that paid more attention to reward than the risk.
Harmon spent two hours with Mickelson on Saturday morning and 90 minutes Sunday morning. He said he is trying to get more flex in his back leg to keep his hips from turning as much. Harmon is equally interested in changing the way Mickelson thinks.
The trick is to get Mickelson to play more conservatively, 'which might be a bigger problem than the swing.'
Three weeks into their relationship, Mickelson was third at the Byron Nelson, third at Wachovia and he won THE PLAYERS. You can imagine how excited he is about the rest of the year and beyond.
'What's most exciting is I feel like we're just getting started,' he said. 'This is only week No. 3. In three months, how much am I going to progress? In three years, where am I going to be? I'm really excited about the direction I'm headed.'