Wozniacki fights pain barrier, Serena into semis

World number one Serena Williams marched into the semi-finals of the WTA Championships on Thursday with a comfortable win over Elena Dementieva while sister Venus kept her title hopes alive long after midnight.

Serena's 6-2, 6-4 victory completed a 100 percent record for the American in Maroon Group and confirmed her as the first player through to the last four at the season-ending showpiece.

Venus, who suffered narrow defeats to Dementieva and Serena in her first two matches, beat Svetlana Kuznetsova 6-2, 6-7, 6-4 in a hard-hitting clash and must now sweat on Friday's results before knowing whether she will be in action at the weekend.

Feisty teenager Caroline Wozniacki remained undefeated on her debut at the $4.5 million Championships after beating Russian stand-in Vera Zvonareva in a White Group match that at times resembled a hospital casualty department.

The 19-year-old Dane eventually won 6-0, 6-7, 6-4 but played the last four points virtually on one leg. She was in tears after suffering agonising cramps in her heavily-bandaged left thigh and could barely hobble to the net to shake hands.

Zvonareva, a replacement for fellow Russian Dinara Safina who withdrew with a back injury, was also in the wars, needing treatment in the second set as blood oozed from her nose.

The Russian later withdrew with an ankle injury meaning second reserve Agnieszka Radwanska of Poland will get a run out against semi-final hopeful Azarenka on Friday.

"I have absolutely no idea how I pulled it through, but I'm very happy about it," said surprise US Open runner-up Wozniacki, who may still need to beat Serbia's Jelena Jankovic on Friday to clinch a semi-final spot."

"I'm gonna do everything I can to get ready for tomorrow," added the world number four. "I'm just going to do everything that physio and the doctors are saying, drinking a lot of fluids, eat some good food, stretch, get some massage, get some ice massage, take a salt bath, everything."

There were no such dramas for Serena who recovered from an early service break to win seven games in a row against Dementieva, a player she had lost to three times this year.

SERENA FATIGUE

Dementieva's cause was not helped by 10 double faults but the Olympic champion can still reach the semi-finals here for the second year in succession by beating Kuznetsova on Friday.

Serena's three wins in three days means the others are scrapping for second spot. Venus's late victory means that should Kuznetsova beat Dementieva they would all have one victory and calculators would be needed to see who survives.

"It feels good to be through because I've never really done well in this round-robin format," Serena, who won the tournament in 2001 when it was a conventional knockout draw, said at courtside. "Tomorrow I'm going to sleep all day because I've played every day so far here and I'm really tired.

Wozniacki, who needed a minute under three hours to subdue Azarenka on Wednesday, looked set for a quick victory when she raced through the opening set against Zvonareva.

Things got worse for Zvonareva in the second set when she developed a nose bleed but, like a boxer with a cut, she suddenly came out fighting and clawed back a 5-2 deficit.

A brutal baseline struggle developed on another breathless night in the Qatari capital with both players scampering around the court to retrieve seemingly lost causes.

Wozniacki should have finished it at 6-5 when she had two matchpoints but Zvonareva got lucky with a Hawkeye challenge and then edged a tiebreaker to set up a deciding set.

After a 10-minute heat break Wozniacki built a 3-1 lead courtesy of a stunning pick-up off a Zvonareva drop shot but the match was taking its toll and she needed treatment on her thigh.

Zvonareva levelled the decider at 4-4 only for Wozniacki, whose leg bandage was now in tattered and torn, to win the next game to allow her to serve for victory at 5-4.

The real drama was just starting though. After missing a forehand at 30-15 Wozniacki was pole-axed by cramp, writhing in pain on the purple concrete as her worried parents and a colourful contingent of Danish fans watched on.

Somehow she dragged herself upright but lost the next point to trail 30-40. She then showed real guts to match Zvonareva shot for shot and win the next three points, clinching victory ater two hours 48 minutes when Zvonareva fluffed a forehand.