London:Rafael Nadal made a successful transition to grass on Wednesday, beating Juan Martin del Potro of Argentina 6-4, 6-4 in the second round at Queen's Club.
Defending champion Lleyton Hewitt was upset by French qualifier Jo-Wilfried Tsonga 7-6 (5), 7-6 (2), while third-seeded Fernando Gonzalez was stretched by Janko Tipsarevic of Serbia before the Chilean advanced 7-6 (7), 4-6, 7-6 (7).
Fourth-seeded Novak Djokovic beat Robert Kendrick of the United States 3-6, 6-3, 6-2.
Nadal, the French Open champion, broke Del Potro in the ninth game of the first set, and then again to open the second.
"It's a big change from clay to grass, but I feel good," the top-seeded Nadal said. "The final last year in Wimbledon gave me a lot of confidence, and I'm feeling well."
Nadal, who has won three straight French Open titles, lost to top-ranked Roger Federer at Wimbledon last year.
"(Del Potro) started serving very well but he stopped a little bit and I could start to return more balls," Nadal said. "But I was calm because with my serve I was winning the games ... and that's important _ especially on grass."
Nadal said he felt relaxed at the Wimbledon warm-up.
"I am coming here with not much pressure ... try to play good tennis, try to adapt as fast as possible to grass," Nadal said.
Sixth-seeded Hewitt, who also won here three straight years from 2000-02, was unable to break down Tsonga's big serve.
Hewitt lost the first set, then broke to lead 2-0 in the second. But the 121st-ranked Tsonga broke back in the seventh game and again for 6-5 when Hewitt netted an easy backhand volley.
Hewitt broke to take the match to a tiebreaker in which Tsonga conceded just two points.
"Physically I feel pretty good at the moment, just didn't quite take my chances out there today," Hewitt said. "He served big into the corners. Even his second serve didn't let me dictate whatsoever."
Djokovic advanced by beating Kendrick, who slipped and hurt his left knee in the second set.
"I was very careful how I move because usually on clay you slide, and here you cannot slide," Djokovic said. "You could see that Robert got a little injury. It could have been more serious. He was lucky."
Djokovic, a semifinalist at the French Open, made several errors early in the match, but he earned a break in the second set after Kendrick's three double-faults. The American slid and twisted his knee in the next game.
"I'm happy to win considering the fact that this is my first grass-court season match," Djokovic said. "I didn't get an easy draw. I played against a player who plays really well on this surface."
Also, 14th-seeded Arnaud Clement of France beat Chris Guccione of Australia 6-4, 6-4; Marin Cilic of Croatia defeated Alejandro Falla of Colombia 6-3, 6-4; and Ivo Karlovic of Croatia beat Alex Kuznetsov of the United States 2-6, 6-2, 7-6 (2).
Marat Safin, seeded eighth, lost the first set against two-time finalist Sebastien Grosjean of France. The Russian recovered to take the match into a final set before rain ended play for the day with the score at 6-3, 4-6, 4-4.