Argentina's Juan Martin Del Potro on Friday denied David Ferrer a chance to defend his Japan Open title, beating the top seed in straight sets in the quarter-finals.

The 20-year-old Del Potro -- ranked 12th in the world after a blistering summer with four titles -- powered his way into the semi-finals with a 6-1, 7-5 victory over the Spanish world number five.

In Saturday's semi-finals, Del Potro will play last year's runner-up, Richard Gasquet of France, who easily dismissed 2003 champion Rainer Schuettler of Germany, 6-3, 6-2.

"When you play against a good player ranked number five, if you win easily, it's not normal. I prepared for everything, for every shot," said Del Potro, who captured his maiden title at Stuttgart in July.

"He runs till the final ball, but I did a good first set. But in the second he started to play better and it was more difficult, but finally I broke him and I went on to win the match."

Del Potro attributed his success since Wimbledon to changes in his game and mindset.

"I've improved a lot. I won two tournaments on hard courts and reached the quarter-finals at the US Open. I did many things to change my game. That's the reason, I think," said Del Potro.

Del Potro never faced a single break point in the first set, but got himself in trouble in the third game of the second set. He double-faulted twice to go down 15-40, but rebounded with two strong first serves to stave off the break.

After breaking Ferrer to go ahead 5-3, he failed to serve out for the match by netting a forehand, but finally finished the match in the 12th game with a forehand winner down the line.

"I tried hard, but Martin, he's very confident. It was not a surprise. He's playing very well these two months. He's been winning a lot of matches, and today he played very good," said Ferrer, 26.

"For me, maybe it was the best match in one month and it's important for me. He served really well on important points. I had a lot of chances to break him in the second set, but he served really well."

In the women's draw, top seed Caroline Wozniacki of Denmark easily beat Thai ace Tamarine Tanasugarn 6-4, 6-1 to set up a semi-final against Jarmila Gajdosova of Slovakia, the winner over Klara Zakopalova of the Czech Republic 7-5, 7-5.

Fifth seed Kaia Kanepi of Estonia edged past Anastasia Pavlyuchenkova of Russia 7-6 (7/4), 7-6 (7/1), while eighth seed Aleksandra Wozniak of Canada defeated Australia's Samantha Stosur 7-5, 6-3 to set up the other semi-final.