Japan's Nishikori routs Fish in Houston

Rising Japanese star Kei Nishikori demolished American number one Mardy Fish 6-3, 6-2 in the quarter-finals of the US Clay Court Championship on Friday.

The 21-year-old Nishikori did not face a single break point in the match as he ousted the top seed from the tournament in stunning fashion.

Nishikori will face Pablo Cuevas of Uruguay in Saturday's semi-finals. Cuevas beat third-seeded Guillermo Garcia-Lopez 1-6, 7-6 (7/4), 6-3.

World number 61 Nishikori hit one ace and five double faults but won 96 percent of first serve points in his first career meeting against Fish.

"I was hitting good returns," Nishikori said. "That's one of the things I did great today. I played good enough to beat him and played good clay court tennis."

"I don't think he played great today, he was missing a lot," Nishikori added.

Despite recently being crowned US number one, Fish has had a mixed year, making two semis in Delray Beach and Memphis but losing in the second round of both the Australian Open and at Indian Wells.

"Being the number one American, it's a responsibility every time you step on the court. People would say 'I'm going to go and watch so and so today and have a pretty good experience doing it,"' Fish said.

"That's a responsibility hopefully I'll have for a little bit and do a better job of it than I did tonight."

Qualifier Ivo Karlovic of Croatia hammered 24 aces in beating fourth-seeded John Isner 7-6 (7/2), 6-7 (2/7), 7-6 (11/9) in a match lasting more than three hours.

The 6ft 10in Karlovic - the tallest player on the ATP Tour - usually towers over his opponents but not this time. He and the 6ft 9in Isner blasted 47 total aces between them.

"Now I know what it's like to play me," Karlovic said. "It's really not easy. I was trying to stay confident even if he was acing me left and right. I tried to stay calm and in the end, I don't know what to say. I was a little luckier. It was a close match."

Karlovic clinched the win with a forehand that clipped the line.

Isner challenged but the ruling stood.

"I knew it was in because I saw it skid," Karlovic said.

Ryan Sweeting of the United States reached his first career semi-final with a 3-6, 6-3, 6-1 victory over Teymuraz Gabashvili.