On Tuesday evening, Kim Clijsters and Sam Stosur turned the tennis serve from an advantage to a disadvantage, breaking each other six straight times to start the third set before Clijsters eventually managed to be broken a little bit less and win. Then Rafael Nadal took the court and played what looked like a completely different sport, continuing his transformation into a dominant server.

Nadal has been unbeatable in his service games at the U.S. Open.Nadal has served in 61 games at this tournament and has won every time, including all 15 against fellow Spaniard Feliciano Lopez, whom Nadal dispatched in straight sets. Nadal has jumped to the top of men’s tennis with his return game, but at the U.S. Open his serve has been his best weapon.
Heading into the tournament, Nadal had won 74% of first-serve points, 59% of second-serve points and 89% of service games so far this year. At the Open, those figures are 85%, 66% and 100%, respectively. Some of that undoubtedly is aided by the fast courts in Flushing. But Nadal has improved his serve more than most. He’s ranking third in the tournament in percentage of first-serve points won, compared to just 22nd on tour this year. Meanwhile, he continues to excel on second-serve points, ranking third in the tournament, compared to first on tour this year. So far during the Open, men have held serve 80% of the time, winning 72% of first-serve points and 51% of second-serve points. Nadal is way ahead of the field.
It hasn’t hurt that Nadal has faced opponents who are mediocre when it comes to returning serve. Lopez and Denis Istomin rank in the middle or bottom at most return stats this year. Nadal’s other two opponents haven’t logged enough match play to make the rankings, but their stats are similarly poor.
Nadal’s serve has helped take pressure off his return game, which has been merely good, not great through four matches. He’s won 35% of break points, 29% of first-serve points, 52% of second-serve points and 20% of return games — all not much better than average for the Open, and well below his marks for the season. That’s against a group of middling to great servers, but none in the top five on tour. As the competition gets tougher — Nadal’s quarterfinal opponent, Fernando Verdasco, has broken serve more often than anyone else in the tournament — Nadal will have to hope his serve remains as effective, particularly if he continues to have trouble returning serve.