Second seed Venus Williams romped to a 6-1 6-1 victory over unseeded Frenchwoman Camille Pin to book a semi-final spot at the Bangkok Open on Friday.

The winner of 36 WTA titles blasted five aces and rarely looked troubled by Pin, who struggled to cope with the ferocity of the American's serves and forehands.

Despite breezing through in straight sets for a third successive match, Williams said her wins were not easy.

"It's hard to keep my concentration and not miss the easy ones," said Williams, who had three double faults and managed to botch a number of simple returns during the 68-minute contest.

"I know I have to be patient but that's not easy because it's my nature to be fast, powerful and aggressive."

Williams reached her third semi-final in as many tournaments and will meet seventh seed Flavia Pennetta of Italy, whom she beat to reach the final of the Korea Open two weeks ago.

Pennetta launched an impressive fightback to beat third seed Shahar Peer 3-6 6-4 6-2 in her quarter-final after a defeat had looked on the cards during the first set.

Pennetta clawed her way back from a set down and took control of the decider as the 16th-ranked Israeli imploded, committing countless errors to go five games behind.

Buoyed up by a few dozen vociferous compatriots in the crowd, Peer had dictated the play in the opening set with powerful serves and solid backcourt returns.

The 53rd-ranked Italian said her match turned around only because she sought treatment for painful blisters on her foot.

"After that, I started to feel better and served much better," she told reporters.

"I was nervous beforehand. She is a good player, she's so confident and I knew it was going to be tough."

Taiwan's Chan Yung-jan beat Polish wildcard Urszula Radwanska 6-2 6-3 and will play China's Zi Yan in the second semi-final.

Zi was given a walkover after defending champion Vania King of the United States pulled out with a back injury.

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