In his five years as a professional, Rafael Nadal has become the uncontested master of clay court tennis, the second-best grass court player in the world, and a consistent threat on hard courts, on which he has won five titles. But when late summer and the U. S. Open roll around, Nadal, invariably, fades.

Some might think this year will be different. Nadal, 21, hasn’t exactly torn up the summer hard court season. He’s still wearing a thin wrap below his right knee, which he injured during his narrow defeat in the Wimbledon final at the hands of Roger Federer. He also retired from a match in Cincinnati two weeks ago after an unexpected dizzy spell. But as this U.S. Open begins, the world no. 2 says he is healthy, rested, and ready to build on what has been the best season of his young career.

“For sure I am here practicing hard. I have good preparation for this tournament,” the Spaniard said over the weekend.

Though it would be a stretch to say that Nadal has remade himself in the last year, he has improved markedly. He still agitates opponents with his left-handed, topspin-laden forehand, and he still extricates himself from perilous positions with speed and hustle. Nadal plays more offense than defense these days, however. He hits flatter, harder shots more often. Even in practice, the difference is noticeable. Yesterday, as fans crowded the top of the bleachers on Court 4 to have a glimpse at Nadal on the furthest practice court from Arthur Ashe Stadium, he hit the ball early and stayed close to the baseline. By Nadal’s standards, this was a brisk session — he doesn’t like to practice more than two hours when a tournament is about to begin. On Friday, he spent four hours on the court.

Federer has noticed the effort. In an interview with Reuters this weekend, the world no. 1 put a damper on all the talk about Novak Djokovic, the world no. 3, as the second favorite to win the U.S. Open, behind Federer himself. Nadal, Federer said, “is better, a lot better to be honest.” He said that if he didn’t win the U.S. Open, he would expect Nadal to take the title.

Paul Annacone, the coach of the soon-to-be-retired Tim Henman and the former coach of Pete Sampras, agreed that Nadal deserves special recognition as the man closest to Federer. Djokovic may have had a breakthrough this summer, when he beat Federer in the final of the Rogers Cup in Montreal, but the 20-year-old Serb hasn’t been a consistent threat, month after month, like Nadal.

“I think Nadal is the one guy who can make Federer better,” Annacone said over the weekend.

People are often surprised that Nadal has adjusted so well to grass — he reached the Wimbledon final the last two years and pushed Federer to five sets this year — yet has never gone beyond the quarterfinals at the U.S. Open or the Australian Open. In his last three appearances in those events, he’s come up against James Blake, Mikhail Youzhny, and Fernando Gonzalez, three players who have similar strengths: great athleticism, a booming forehand, and a talent for hitting Nadal’s shots as soon as they bounce, which gives Nadal less time to react. Though Nadal remains susceptible to this type of player on grass (Youzhny won the first two sets against the Spaniard at Wimbledon this year before his back began to ache), Annacone said the lawns of the All England Club no longer play as quickly as the hard courts at the U.S. Open.

“Wimbledon is slower and the balls are heavier,” Annacone said. “With the way the grass is now and the way Nadal can move, he can still play his game on grass and go from defense to offense.”

The U.S. Open’s moderately fast hard courts present more difficulties. Nadal’s competitors — at least those who have beaten him in the hard court majors — are accustomed to hard courts and practice little on grass, since no one plays on grass these days but for two tournaments a year, at most. Luckily for Nadal, he should have plenty of time this year to adapt and prepare for the difficult opponent, probably Djokovic or Lleyton Hewitt, who he is on track to face in the semifinals.

Nadal first meets Alun Jones, a 27-year-old wild card from Australia. The highest ranked player in Nadal’s quarter is Gonzalez, the Chilean who waxed Nadal at the Australian Open this year, but who has returned to earth since then. Of the remaining men Nadal might face on his way to the semifinals, only two are the sort who can cause Nadal trouble: Dmitry Tursunov, a powerful but unpredictable Russian, and Serb Janko Tipsarevic.

In the last three seasons, the rivalry between Federer and Nadal has become the centerpiece of their sport, and it may one day become the best rivalry the game has ever had, if that’s not already the case. At the French Open, Nadal has defeated Federer three times, twice in the final. At Wimbledon, Federer has won twice, both in the final. In two hard court finals, Nadal has won one time (Dubai in 2006) and Federer the other (Miami in 2005). This year’s U.S. Open gives us the best chance to watch them compete on a neutral — or at least more neutral — surface at a major, with much at stake.

Federer is trying to become the only man in the Open era to win four consecutive U.S. Open titles. He still has three majors to win to catch Pete Sampras and his record of 14. Nadal has an outside shot at the no. 1 ranking, and he knows the road to greatness — rather than the road to “greatest no. 2 player of all time” — requires him to win a major other than the French Open. When you watch Nadal this week, don’t be fooled by his knee or worried by the surface beneath his feet. He’s more ready for the U.S. Open this year than ever before.

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