The French Open champion broke Del Potro in the ninth game of the first set and 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."

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."

Novak Djokovic also advanced, beating an injured Robert Kendrick of the United States 3-6, 6-3, 6-2. The American 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. Kendrick 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."