London - Former US Open champion Juan Martin del Potro admits Japan's Kei Nishikori will pose a serious danger to his Wimbledon hopes in Saturday's third round.
Del Potro eliminated one Japanese star on Thursday as the Argentine battled to a 6-2, 6-3, 1-6, 6-4 victory over Go Soeda and now he has to overcome another in the shape of 19th seed Nishikori.
While Del Potro, who won the US Open in 2009, was complimentary about the challenge posed by world number 58 Soeda, he knows 19th seed Nishikori will be a much sterner test of his form.
Nishikori became the first Japanese man to reach the last 32 at Wimbledon for 17 years after cruising past France's Florent Serra 6-3, 7-5, 6-2.
The 22-year-old, who reached the Australian Open quarter-finals earlier this year, is regarded as one of the sport's brightest young stars and Del Potro, who emerged alongside the Japanese on the junior tour, has no intention of taking him lightly.
"It's going to be difficult match. I've known Kei since juniors and he has improved his game a lot," Del Potro said.
"He had a fantastic year in 2011 and this season he's doing well.
"All his shots are dangerous. He's not a tall player, but he serves really well. Also he's very consistent with the forehands and backhands, and he's very, very fast."
Del Potro, who is gradually returning to peak form after struggling with knee injuries for the last 12 months, is especially concerned about facing Nishikori on grass.
The diminutive Nishikori's game is well suited to the faster surface, whereas the powerful but more ponderous Del Potro prefers to play on clay.
"On grass he's very dangerous, like all the players in the third round," Del Potro said.
"On this kind of surface he has a good advantage and he will be faster than his opponent. That's make him very, very dangerous."
Del Potro was also keen to praise Soeda, who recovered from a nightmare start to push the Argentine hard in the last two sets.
"I'm glad to beat him. We played twice about five years ago and he improved a lot," Del Potro said.
"He started to play much better after the second set and was dangerous for me at the end of the match.
"He plays similar to Nishikori with forehands and backhands, and he's very fast like Nishikori, also."