Hard-hitting Del Potro delivers on grass to see off Nishikori

Juan Martin del Potro has not always been at his best on grass, but the 23-year-old Argentinian delivered one of his finest Wimbledon performances here yesterday to reach the fourth round for only the second time in his career.

Del Potro beat Japan's Kei Nishikori 6-3, 7-6, 6-1 to earn a meeting in the last 16 with David Ferrer, who beat Andy Roddick 2-6, 7-6, 6-4, 6-3.

Del Potro, the world No 9, has been climbing his way back up the world rankings after being out of the game for a year with a wrist injury. He began his comeback 18 months ago and has been enjoying a good year, having reached the quarter-finals of both the Australian and French Opens, where he lost to Roger Federer on both occasions.

Nishikori, the world No 20, represented a major test for the 2009 US Open champion, but Del Potro responded in style.

"It's my best match this week," he said. "I played really aggressive, trying to hit the ball really hard, and I took all my break points. That's important to have the control of the match and play with more focus and be more relaxed. I think I played a very good match today.

"Nishikori is a dangerous player on a grass court. Beating Nishikori three sets in a row, it's important."

Del Potro last played the Japanese three years ago.

"He's playing much better, for sure," Del Potro said. "Maybe he had a little bad luck today in the tie-break. If he had won that set we would still be playing."

The Argentinian said the windy conditions were "horrible".

He added: "It was the same for both players. That's what I was trying to think. If I made a mistake, he could also make one. I was trying to play as best I could because the windy conditions are tough to play."

Del Potro's season has been interrupted in recent weeks by a knee injury, which also scuppered his chances of pulling off a major shock at the French Open last month, when he led Federer by two sets before losing in five.

The Argentinian said his knee was now "almost perfect". He added: "I had a very good recovery at home [after Paris] and now I'm getting better every day. So it's important for this tournament and for the rest of the season."

Del Potro said he still felt at his most comfortable playing on hard courts, but feels he is improving on grass.

"It's good to have time playing on grass – and also for the Olympics," he said. "I'm playing better day to day, training hard on grass courts for this tournament and for the Olympics as well. If you win matches, the sensation is more comfortable for me. But, anyway, it's a difficult surface for the Argentinian players."

Does Del Potro think he is getting close to the heights he scaled in 2009, when he won the US Open?

"I don't know if I'm playing better or similar or worse than 2009," he said. "I'm top 10 and having a good season this year. I'm looking forward to the rest of the season, trying to get closer to the best players in the world."

Roddick, meanwhile, has had a miserable year, dogged by injury, though he won the title at Eastbourne last week and had not dropped a set in his first two matches here, against Jamie Baker and Bjorn Phau.

Ferrer, however, proved a much tougher proposition. Roddick won the first set and had chances in the second set tie-break, but Ferrer then took charge.