SINGAPORE (Reuters) - 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 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."
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 sets 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 at 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, smashed 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 then 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 get out of the hole, she finally got herself on the board in the ninth game as she held serve to make it 2-1.
Williams 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 reveled.
She stepped away from her traditional counter-punch game and went on the front foot, landing attacking groundstrokes 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.
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.
Additional reporting by John O'Brien; Editing by Sudipto Ganguly and Ken Ferris