Williams walloped by Halep

Singapore - 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 on Wednesday.

As well as Halep played in moving her opponent back and 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 plays Ana Ivanovic later on Wednesday, to make it through to 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."

Williams gave no indication of the struggles that awaited her as she boomed down an ace to start the match between the two players who were impressive in claiming straight set victories in their opening Red Group matches.

That ace would be one of only nine points the 18-times grand slam champion would win in the opening set as her game fell apart to give Maria Sharapova hope of overhauling her to finish the season as world number one.

Halep, serving supremely, needed only 12 minutes to race 4-0 ahead with Williams looking almost in shock and her routine failure to send simple groundstrokes over the net.

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 Romanian, runner-up at the French Open earlier this year, grew in confidence as Williams offered little hope of a recovery. Halep, who beat Bouchard in her opener on Monday, smashing an ace to take the set 6-0 at the third opportunity.

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

Jumping around in between points and screaming at herself in an attempt to snap out of the hole, she finally got herself on the board in the ninth game as she held serve to make it 2-1.

She then rallied on the impressive Halep serve to force a break point but the 23-year-old Romanian snuffed it out with another ace and went on to make the key hold for 3-1.

Rather than feel the heat as the victory line approached, Halep revelled.

She stepped away from her traditional counter-punch game and went on the front foot, landing attacking ground strokes to move Williams around the court as she moved 5-2 ahead with the American despondent.

She claimed the famous win on her first match point, when Williams dumped another forehand into the net as she matched her career worst two game total from a 1998 defeat by Joannette Kruger in Oklahoma City.

"The biggest match of my life. I'm really happy," Halep said after becoming only the second woman to beat Williams in straight sets in a WTA Finals match after Kim Clijsters in 2002.