Virus forces Ivanovic withdrawal

Ana Ivanovic admitted she was too ill to continue after withdrawing from the season-ending Sony Ericsson WTA Tour Championship in Doha.

The 20-year-old, who has been plagued by a virus, withdrew before her final round robin match against Svetlana Kuznetsova on Friday.

'It's obviously, very, very hard for me,' the Serbian, who was on her way out of the tournament anyway after losing her first two matches to Jelena Jankovic and Vera Zvonareva, told her official website.

'After the other night's match I started to actually feel worse. Yesterday I didn't feel good, and today even worse.

'I tried to hit yesterday actually. I was on the court for about 10 minutes, and as long as I didn't move it was okay. But if I tried to hit a little bit harder or to move on the side, it was impossible to do.'

Serena Williams also pulled out with a stomach muscle injury before her match with Elena Dementieva.

Williams, who lost 7-5 1-6 0-6 to sister Venus on Thursday, would have made the semi-finals if she had beaten Dementieva.

She said: 'I had zero pain (during Thursday's match), like zero pain. The moment I got home, I did feel pain, but in the match I didn't feel pain at all.

'When I woke up (Friday), I was in pain just getting out of bed. I've had this before, so once I felt the pain it was like red flags.

'I'm having a great time, a great career. I'm doing so well, it's not worth it. Today when I practised I was in pain when I played the groundstrokes so I didn't want to risk it.'

This is the second straight year that Williams has pulled out of the event - she played just a set last season before retiring with a knee injury.

Zvonareva was in action on Friday though and she capped a surprising run at the Khalifa International Tennis Complex by securing an impressive 2-6 6-3 6-4 victory over Jankovic to claim top spot in the White Group.

The lowest seed in the eight-player field, Zvonareva finished the group stage with a perfect 3-0 record, a complete reversal of her first appearance at this event when she went winless.

'It feels great, of course,' said Zvonareva, who missed much of 2007 due to a wrist injury. 'I worked hard to get into these championships, and I'm really happy to be here and to play against the eight best players in the world. And it's great that I was able to come up with some good tennis so far.'

Jankovic though felt she had let her opponent back into the match.

'I was playing very well in the first set, but then I completely let my opponent play her game,' Jankovic told the WTA's official website.

'I didn't serve very well and I didn't return very well, and Vera can rally all day long without making many mistakes.'

Zvonareva will face fellow Russian Dementieva in the semi-finals, while Venus Williams will meet world number one Jankovic.

There were two dead-rubber matches also played on Friday featuring reserve players Nadia Petrova and Agnieszka Radwanska.

Russian Petrova replaced Serena Williams for the final Maroon Group round-robin match and was beaten 4-6 6-4 4-6 by Dementieva, while Radwanska, from Poland, stepped into Ivanovic's shoes for the scheduled match against Kuznetsova in the White Group and won 6-2 7-5.

The final will be played on Sunday, with the winner walking away with a cheque for US$ 1.34million.