Top seed Andy Roddick [Images] beat impressive Japanese teenager Kei Nishikori 6-2, 6-4 in the second round of the San Jose Open on Thursday.

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Nishikori won his first career title last week in Delay Beach but was no match for Roddick, who relied on a huge serve and solid play at the net to see off the 18-year-old.

In other second round matches, towering American John Isner fought off three match points to upset third seed Tommy Haas 4-6, 7-6, 6-3, while second seed James Blake moved on with a 6-3, 6-4 victory over Jesse Levine.

Roddick said it was one of the best matches he had played in over the past six months and that he knew he needed to step up a level to dispense with his young opponent.

"I was tight about this match," Roddick said.

"I watched him yesterday and he was crushing the ball. So I was going to try to use everything to try to get a win out there. I was very impressed with him. I think he's going to be a player."

After Roddick took the first set 6-2, the two traded early breaks in the second. Nishikori then committed three unforced errors in a row to lose the set 6-4 and hand Roddick victory.

"I'm not feeling good," Nishikori said.

"I made too many easy mistakes. I had so many chances. I didn't play well."

Roddick will face another American, Mardy Fish [Images], who beat Germany's [Images] Denis Gremelmayr 6-7 6-3 6-3.

Isner was down 6-3 in a second set tie-break but the 6ft 9ins (2.057 metre) American fired down two huge serves and then pushed Haas back deep in the court and charged.

Haas flung a forehand passing shot attempt long.

Isner then coolly snapped up the next two points to take the set.

"He hit a really good serve that kind of jammed me and I tried to get away from it and hit a backhand deep and forced a mistake and that was big," said Isner of the third match point.

"From there, I had nothing to lose because I was already down three match points and I played pretty loose and some of my best tennis."

Isner needed just a single break in the third and had all the momentum, serving out with two aces and two service winners to take the contest.

Isner will face Spain's Guillermo Garcia-Lopez in the quarter-finals.

Taiwan's Lu Yen-hsun overcame American Wayne Odesnik 6-4, 6-4 and will play fourth seed Radek Stepanek.

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