Not that long ago — five years, to be exact — you could argue that David Nalbandian might become a better tennis player than Roger Federer. These days, such a preposterous comment would inspire derision and rightfully get you laughed out of whatever room you happened to be in, though perhaps not until you agreed to never speak about tennis again for as long as you lived.

In 2002, though, Nalbandian and Federer were the two most talented youngsters in the game, and Nalbandian seemed to have just as much going for him, if not more. Who would have the better career was anyone’s guess.

Nalbandian, five months younger than Federer, had beaten his rival in the 1998 junior U.S. Open final and had a knack for dulling Federer’s stylish — and in those days, less consistent — game with an efficient, sensible brand of tennis. Nalbandian has never been much for artistry: He hits a two-handed backhand as well as anyone ever has, but the trademark of a great two-hander, unlike the flashy one-hander, is that it doesn’t look like much. His serve was adequate, as was his speed around the court. Nalbandian had great hands, though, and an uncanny ability to hit precise shots at unlikely angles no matter what his opponent sent his way (those of you who admire Andy Murray might notice the similarities).

In mid-2002, Nalbandian, then 20 years old, surprised the tennis world by reaching the final of Wimbledon. What was an Argentine doing in the Wimbledon final? (Don’t those guys die if they stay off clay for too long?) Lleyton Hewitt, then the no. 1 player in the world, dismissed Nalbandian in straight sets, but at least the young Argentine was there. Federer had lost in the first round that tournament, a terrible disappointment after he defeated defending champion Pete Sampras on his way to the quarterfinals in 2001. At that moment in history, it looked as if Nalbandian would be the steadier player and Federer the more flamboyant and erratic one, the kind who could beat a great player (Sampras) just as easily as he might lose to a has-been (think Richard Gasquet).

At the end of 2002, Nalbandian was ranked no. 12. Federer was ranked no. 6. Nalbandian had two titles to his name, Federer four. They played twice that year, and Nalbandian won both times. He won their next three meetings, too, including the fourth round of the 2003 U.S. Open, a tournament that Nalbandian should have won (he led Andy Roddick two sets to none in the semifinals and had control of the third-set tiebreaker before he pulled a stomach muscle and lost in five sets). Had he won that event, these two up-and-comers would have had a major title each, with great futures ahead of them.

Of course, we now know how it turned out. It’s been so bad for Nalbandian that his surprise victory over Federer yesterday in the Madrid final, 1–6, 6–3, 6–3, is a mere asterisk attached to 20 positively dreadful months of tennis. Since their nearly identical early days on the tour, these two men could not have had more different careers: one man essentially a bust, and the other on his way to becoming the greatest player the game has ever known, no questions asked. Nalbandian has won four titles since 2002 for a grand total of six. Federer has racked up another 47 for a haul of 51. After rising to as high as no. 3 in the world, Nalbandian’s ranking had fallen to 25 before this event; Federer hasn’t been less than no. 1 since January of 2004 . Nalbandian’s personal streak against Federer is long gone, too: After winning their first five meetings, he lost eight of their next nine. He’s no richer for his failures, either, as his $8 million in prize money — compared to nearly $36 million for Federer — attests. This weekend, Nalbandian, now 25, showed that he has incredible tennis left in him, if he cares to let it out. Before Madrid, the Argentine had a record of 19–17 on the season, no better than a player such as Hyung-Taik Lee of Korea, whose 25–23 record this year has vaulted him to no. 44 in the rankings, eight spots from his career high. After Madrid, he is the third man in the history of the tour, and the second this season, to defeat the top three players in the world on the way to a title (Nalbandian destroyed Rafael Nadal earlier in the week, 6–1, 6–2, and then dispatched Novak Djokovic in the semifinals).

Nalbandian hired a new coach this summer, Martin Jaite, after going without one since last year. He has a new physical trainer, too. Put those together with his much improved play last week, and we have a classic “rebirth” story, so often told in sports and especially in tennis, where every victory and defeat is magnified because each one falls squarely on one person’s shoulders (no teammates to blame in tennis).

But it’s still much too early to say that Nalbandian is back, or even on his way to being a reasonably successful player again. He’s still in worse shape than he ought to be, and it’s doubtful that the poor work ethic that did him in the last few years has suddenly disappeared. And don’t forget that he has starred in this comeback role before.

Remember the season-ending Masters Cup in 2005? Nalbandian trailed Federer two sets to none before carving up the world no. 1 with crisp backhands and his long-underrated front-court skills — he might not hit pretty volleys or do a lot with exceptionally difficult volleys, but when given a reasonable volley, Nalbandian rarely disappoints. It seemed like a defining moment, and the confidence he gained from it carried him to the semifinals of the 2006 Australian Open. There, he won the first two sets against Marcos Baghdatis and promptly imploded. He’s been getting worse ever since. Don’t be surprised if it happens again.

Mr. Perrotta is a senior editor at Tennis magazine. He can be reached at tperrotta@nysun.com.