It was almost a year ago that many tennis fans in the United States had their first extended look at Rafael Nadal, the 19-year-old sensation from Spain who right now gives world no. 1 Roger Federer more trouble than any other player on tour.

The setting was the ATP Masters Series event in Miami, and Nadal dazzled and danced his way into the final. Through nearly three full sets of a fivesetter against Federer, the Spaniard perplexed the world no. 1 with spin, angles, speed, and impossible agility. And though he lost the match – still his only loss against Federer in four tries – he proved he could beguile on hard courts, not just his native clay. When 2005 came to a close, Nadal had won 11 titles, including the French Open and three on hard courts, and posted a 78-10 record, earning him the no. 2 ranking and a reputation as the best young player since Mats Wilander.

The questions for 2006 and beyond are: How much can he improve, and how long can he last? At this week’s hard court tournament, the Pacific Life Open in Indian Wells, Calif., Nadal shows no signs of giving up any ground. He defeated Federer, in Dubai, in his second tournament of the season, and yesterday moved into the third round at Indian Wells with a 6-4, 6-4 victory over Jan Hernych of the Czech Republic. He says his serve, still his weakest shot (though aided by the fact that he is lefthanded), has improved, and his serving statistics already were among the best on the tour last year (he held serve 84% of the time). Nadal’s return game is excellent, and in terms of intensity, concentration, and competitive spirit, he is among the game’s elite.

One other weakness is the lack of depth on his groundstrokes, which too often land short of the baseline, but his heavy topspin usually prevents this from hurting him (one noteworthy exception was his loss to James Blake at last year’s U.S. Open).

Longevity is another matter, and anyone who enjoys watching Nadal – frankly, it’s near impossible not to – can only hope for the best. The Spaniard plays a brutal brand of tennis, and no matter how much credit his unorthodox topspin forehand receives, his feet are responsible for his success. Many of the world’s best tennis players move with uncommon speed and grace, but no one is as explosive as Nadal, especially considering that he carries the frame and the muscle of an NFL cornerback. Nadal stands 6-foot-1 and weighs 188 pounds – compare that to the only man who might get around the court more quickly, the 5-foot-9, 152-pound Guillermo Coria. Coria is a waterbug; Nadal is a bull.

It’s no surprise, then, that Nadal is hard on his feet. During the final months of 2005 and the first two months of this season, severe pain in his right foot forced him to miss the year-ending Masters Cup and this year’s Australia Open. At times, Nadal said, he wept over an injury he thought might spell the end of his career.

The trouble began during his title run at the Madrid Masters in October, where he won the final in five sets after losing the first two. At first, Nadal feared he had injured his right foot as he had a year earlier, when he sustained a stress fracture. But doctors could find no sign of a new fracture. Finally, in January, Nadal learned for certain that he had no fracture, just inflammation in one of his tendons. He would have to adjust his shoes to accommodate the stress he put on his feet. He also felt some pain in his knee for the same reason.

“The problem is how he stands up and how he runs. He puts a lot of pressure on his foot,” Benito Perez-Barbadillo, an ATP Tour official based in Monaco who is close to Nadal, said. “We went to Nike headquarters and had a special shoe done for him.” For a man his size, Nadal has small feet (he wears a size 9 – sneaker). His feet are quite wide, however – as Perez-Barbadillo puts it, “like a good soccer player.” Since he received his new shoes from Nike, Perez-Barbadillo said, Nadal has felt no pain.

There’s something else Nadal can learn to do to take some pressure off his feet: play less often. In 2005, he played 22 tournaments; Federer, in comparison, played 15 (he won 11 of them). Though this translates to roughly the same number of matches (Federer played 85 to Nadal’s 88), the world no. 1 had more off weeks. This year, Nadal has 22 tournaments on his calendar, not including the year-end Masters Cup, for which he will almost certainly qualify. Don’t be surprised if he trims this schedule, perhaps dropping a clay-court event in Hamburg, prior to the French Open, and another in either Sweden or Germany after Wimbledon. He might consider backing out of the World Team Championship in Germany before Roland Garros or a hard-court event after the U.S. Open, as well.

Nadal loves to play, but he will need to play a little less as he moves into his mid 20s, lest he end up more like Gustavo Kuerten (now 30 and a shadow of his former self after repeated hip injuries) or 26-year-old countryman Juan Carlos Ferrero, who won the French Open and reached the final of the U.S. Open in 2003, and has done nothing since. Of course, that’s the future. Until then, enjoy Nadal in his present form, full of energy and daring and having enough confidence to defeat anyone, even the man who might one day be remembered as the greatest player of all time.

tperrotta@nysun.com