Italy's [Images] Flavia Pennetta knocked out second seed Sania Mirza [Images] of India to advance into the semi-final of the US $175,000 Japan [Images] Open Tier III WTA event in Tokyo on Thursday.

The Indian went down 4-6, 4-6 to eighth-seeded Pennetta in the quarter-final in an hour and 19 minutes.

- I have learnt to be mentally tough: Sania

Sania squandered a quick start, when she led Pennetta 2-0 in the first set to lose four games in a row. The Indian found it difficult to stem the slide and barely managed to win the seventh game on her serve to close the gap to 3-4.

In the second set, Pennetta earned a break of serve in the seventh game and served out the match at 6-4.

Wimbledon champion Venus Williams powered into the Japan Open semi-finals with a 7-6, 6-3 win over Australia's Alicia Molik [Images] on Thursday, while Lleyton Hewitt [Images] booked a spot in the men's quarters by beating Spain's Ivan Navarro.

Williams's superior athleticism gave her the edge in the first-set tiebreak, which she took 7-4, and the women's top seed was never seriously troubled in the second.

The American wrapped up the quarter-final in one hour, 33 minutes, letting out a scream as she ripped a forehand return crosscourt on her first match point.

Williams, winner of last week's Korean Open, has now won 18 of 20 matches since capturing her sixth grand slam singles title at Wimbledon.

"I'm just doing what it takes to win," the former world's best player told reporters.

"Sometimes I played some impressive tennis, sometimes my errors hurt me. I'm just trying to stay positive, whatever it takes."

Williams will face unseeded Caroline Wozniacki in the last four in Tokyo after the Dane's 6-3, 2-6, 7-6 win over Czech Klara Zakopalova.

In the men's draw, Hewitt eased past Navarro 7-5, 6-3 but the Australian, who won the Japan Open in 2001, faces a stern test against big-serving Croatian Ivo Karlovic next.

Seventh seed Karlovic scraped past Asia's number one Lee Hyung-taik 7-6, 6-7, 7-6 in an epic struggle lasting two hours, 38 minutes.

Spaniard Fernando Verdasco, the eighth seed, battled past former Australian Open champion Thomas Johansson of Sweden 7-6, 5-7, 6-3 to book his place in the quarter-finals.

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