Simona Halep handed an out-of-sorts Serena Williams the joint heaviest defeat of her long and illustrious career as the Romanian beat the world number one 6-0, 6-2 at the WTA Finals.

As well as Halep played in moving her opponent around Singapore's purple Indoor hardcourt, the 33-year-old American only had herself to blame for the defeat after her serve fell apart and the errors flowed.

The loss halted the double defending champion's winning streak at the season-ending event at 16 matches and leaves her needing to beat Eugenie Bouchard, who later lost 6-1, 6-3 to Ana Ivanovic, to reach the last four from the Red Group.

"It was actually embarrassing I think describes the way I played. Yeah, very embarrassing," Williams told reporters, before heaping praise on Halep.

"I've seen her play a lot. Like I said, she's never played like this before."

The American, looking for a fifth WTA Finals title, also tossed in six double faults with the few second serves that did make it over getting rough treatment from Halep.

The last time Williams lost a set 6-0 was in Madrid last year at the hands of Anabel Medina Garrigues, but then she bounced back to win the match and the tournament. That scenario never looked like repeating itself on Wednesday.

Heading into the final round of matches, all four players can still advance from the Red Group although Halep is virtually assured of qualifying after winning her first two matches while Williams and Ivanovic have a win and loss apiece.

Bouchard faces an almost impossible task to reach the semi-finals after two heavy straight sets defeats but is still mathematically in with a chance of advancing.

Source: Reuters