Last updated on .From the section Tennis

Sharapova claimed her 20th career win at the WTA Finals

World number four Maria Sharapova held her nerve in a tense finish to beat top seed Simona Halep and close in on a last-four place at the WTA Finals.

The Russian withstood a Halep fightback to win 6-4 6-4 and move top of the Red Group in Singapore.

US Open champion Flavia Pennetta earlier beat Agnieszka Radwanska 7-6 (7-5) 6-4 to keep her hopes alive.

Pennetta and Sharapova will meet in the final round of Red Group matches on Thursday, with Halep facing Radwanska.

All four players remain in with a chance of securing one of two semi-final places.

World number one Serena Williams is absent from the eight-player field in Singapore as she recovers from injury.

Sharapova shows true grit

Five-time Grand Slam champion Sharapova showed her quality and fighting spirit as she built a commanding lead, and then gathered herself as Halep came battling back.

Sharapova, completing only her second full match since Wimbledon following injuries, led 6-4 5-1 but failed to convert two chances to serve out the match.

Halep had her chance to level on serve, only for Sharapova - after a pep talk from coach Sven Groeneveld - to rediscover her attacking intent and fire away a backhand on match point.

"I'm quite pleased to be able to beat the number two player in the world," said the 28-year-old, who took her career record against Halep to 6-0.

"I don't think that I played unbelievable tennis today. I still made errors, but cut down on my errors from the first match."

Pennetta keeps hopes alive

Flavia Pennetta is currently ranked eighth in the world

The Italian, 33, knew that a second defeat of the week would see her eliminated and it brought out her best performance since winning a first Grand Slam title in New York last month.

Pennetta, who could play her last ever match on Thursday before she retires, fought back from 5-3 down in the first set to win in one hour and 40 minutes.

"Of course it was important today to win this match, because like this I still have a little bit of chance, no?" said Pennetta.

Radwanska said: "Definitely the first set I should have won. The concentration was slipping away sometimes and I wasn't focused enough."