Ecstasy and euphoria are the usual emotions world No.1 Serena Williams experiences on a tennis court.

Yesterday, she encountered a different one - embarrassment. One of the game's all-time greats, a winner of 18-grand slam singles crowns, 63 WTA titles, the owner of four Olympic gold medals, Williams has become accustomed to success.

But on Singapore's purple indoor hard court, Simona Halep, left, took her back 16 years to a time when, as a teenager, she was trying to make a name for herself. Halep's 6-0, 6-2 success in their Red Group clash at the WTA Finals was the worst defeat Williams had experienced since she was crushed 6-1, 6-1 by Joannette Kruger in the quarter-finals at Oklahoma City in 1998.

Halep served well, pushed her opponent around the court and went for her shots, but Williams, by her own admission, was woeful.

"Yeah, my forehand was off today again. I guess it went on an early vacation. Lord knows my serve was as well. My serve was at best in the 10 and under division in juniors. Embarrassing I think describes the way I played."

Williams had shown no sign of what was to come as she held of the feisty challenge of Ana Ivanovic to start her campaign on Monday with a 6-4, 6-4 victory, her 16th consecutive win in the season-ending championships. She faces Canada's Eugenie Bouchard today with a place in the semi-finals on the line. Bouchard fell 6-1, 6-3 to Ivanovic yesterday.