Simona Halep... impressive.

Simona Halep handed an out of sorts Serena Williams the joint heaviest defeat of her illustrious career as the Romanian beat the world no.1 6-0 6-2 at the WTA Finals yesterday.

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 Bouc-hard to make it through to the last four from the Red Group.

“It was actually embarrassing the way I played. Very embarrassing,” Williams told reporters, be-fore 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.

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 yesterday.

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

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.

Other result: Ivanovic bt Bou-chard 6-1 6-3.