Venus and Ivanovic into Zurich semi-finals

Venus Williams survived an inconsistent performance to defeat Italian Francesca Schiavone 6-3, 6-3 and reach the semi-finals of the Zurich Open overnight.

The third seeded American struggled to overcome a tenacious opponent in an untidy match that was riddled with errors from both players, but also featured some well-contested rallies and spectacular shot-making.

Five consecutive service breaks ended with Williams leading 5-3 after Schiavone double-faulted to leave her serving for the first set.

In the second, Williams broke again to lead 1-0, but she had to fight off two break points in the next game and then needed four game points to hold for 3-1.

Following an exchange of breaks in the next two games, Schiavone held and then was unable to convert any of three break points to level at 4-4. After Williams held for 5-3, a strong return forced Schiavone to net a forehand and drop her serve on match point.

"She's a good competitor and she went for a lot out there today, sometimes maybe a little too much, but if a lot of those balls went in it would have gone well for her. But it went well for me," said Williams.

Williams will next face second seeded Serb Ana Ivanovic, who defeated Czech left-hander Petra Kvitova 6-1, 6-4.

It is the first time since Wimbledon that the Roland Garros champion has won consecutive matches.

Kvitova forced Ivanovic to save two break points in the early stages of the match but her serve let her down, and two consecutive double-faults gave Ivanovic a break for 3-1.

And although Kvitova recovered from 1-4 to 4-4 in the second set, a ninth double-fault gave Ivanovic a decisive break for 5-4.

Italy's Flavia Pennetta followed up her victory over top seed Jelena Jankovic by beating Katarina Srebotnik of Slovenia 7-5, 6-2.

One aspect of her game that allowed Pennetta to recently rise to a career-high ranking of 15 is her improved serve, and she says that has played an important factor in her progress to the Zurich semi-finals.

"My serve has improved a lot," she said. "It makes a lot of difference to win a few points with no play, just rest, is good. Now I understand how the men feel."

Pennetta will now play Spaniard Anabel Medina Garrigues, who reached her fifth semi-final of the season when opponent Victoria Azarenka of Belarus retired after pulling a chest muscle.

The incident occurred after Azarenka had won the first set 6-4 and as she lost a point to go down 5-3 in the second. Azarenka attempted to continue after treatment, but retired after losing her serve and the set 6-3. ends