Juan Martin del Potro upset top seed and defending champion David Ferrer in Friday's quarter-finals of the Japan Open.

The Argentinian won four consecutive tournaments during July and August before being ousted in the quarter-finals of the US Open by eventual runner-up Andy Murray.

The world number 12 has resumed his fine run of form at this hardcourt event following a pair of singles wins against Russia in the Davis Cup semi-finals.

After a victory over 11th seed Jarkko Nieminen in the third round, Del Potro seized an early lead against Ferrer and never looked back on his way to a 6-1 7-5 win.

The 20-year-old did not face a break point in the first set, but brought up five of his own, winning three.

Things were not as easy in the second set as Ferrer earned eight break-point opportunities.

The fifth-ranked Spaniard managed to win only one, however, as Del Potro closed out the match in one hour 39 minutes.

Del Potro advanced to face fourth-seeded Richard Gasquet of France, who earned a 6-3 6-2 victory against 12th seed German Rainer Schuettler.

Third-seeded Chilean Fernando Gonzalez also fell short of the semi-finals.

Ninth seed Czech Tomas Berdych steamrolled to a 6-0 6-4 victory against Gonzalez, setting up a meeting with second-seeded American Andy Roddick, who moved one step closer to his second straight title with a 6-3 6-4 victory over unseeded Viktor Troicki of Serbia.

Troicki advanced to the quarters when seventh-seeded Frenchman Jo-Wilfried Tsonga retired with an abdominal strain during their match on Thursday. Unfortunately for Troicki, Roddick was healthy and up to the task.

Roddick, who won his 26th career title on Sunday at the China Open, fired seven aces and cruised to the final four in one hour 20 minutes.

World number eight Roddick has won two of three lifetime meetings against Berdych, who earned his only victory during their first clash at Madrid in 2006.

In the women's event, top seed Caroline Wozniacki booked a spot in the semi-finals with a 6-4 6-1 victory over seventh seed Tamarine Tanasugarn of Thailand.

The world number 16, Wozniacki won her first two career titles at Stockholm and New Haven in August before making a respectable run to the fourth round at the US Open.

However, the Denmark native was ousted in the first round in her last two appearances, at the Pan Pacific Open and in Beijing.

Wozniacki's return trip to Tokyo has been far more successful. She advanced to the final four with a carefree win against Tanasugarn in a match that lasted one hour 37 minutes.

The 18-year-old will next face lucky loser Jarmila Gajdosova of Slovakia, who forged a 7-5 7-5 triumph over Czech Klara Zakopalova in their quarter-final match.

In the bottom half of the draw, fifth-seed Kaia Kanepi overcame seven double faults to earn a 7-6 (7-/) 7-6 (7/1) win against Russian Anastasia Pavlyuchenkova.

The Estonian advanced to take on eighth seed Aleksandra Wozniak of Canada, who cruised to a 7-5 6-3 victory against Australia's Samantha Stosur.