SINGAPORE - One day after suffering her heaviest defeat since she was a teenager, Serena Williams was back to her brilliant best as she swatted aside Eugenie Bouchard 6-1 6-1 in her final round robin match at the WTA Finals yesterday.

The world number one was humiliated 6-0 6-2 by Romania's Simona Halep on Singapore's purple hard court on Wednesday but put herself on the brink of a semifinal berth with the crushing victory over her hapless Canadian opponent.

Williams, who beat Ana Ivanovic in her opening match on Monday, has two wins and a loss and needs Halep to win one set against the Serb to advance to the last four.

Ivanovic faces Halep in the final group game today.

Halep is already assured of her place in the semis, while Bouchard has been eliminated from the tournament after three straight defeats.

Williams appeared lethargic and lacking motivation in her defeat against feisty counter-puncher Halep but made sure there would be no repeat of her "embarrassing" loss against the youngest player in the elite eight-woman field.

The 33-year-old forced three break points immediately and while Bouchard battled back to win a game that ensured Halep advanced to the semifinals, Williams exuded focus and aggression as she set about dismantling her opponent.

"Yesterday was tough for me but I had to put that behind me and my coach really helped me to recover from that," Williams said in a courtside interview.

"He told me I needed to focus on today and that I was still in the tournament. I actually felt like I was out of the tournament so it was good advice."

Williams gave the 20-year-old a tennis lesson she would not forget over the course of the 59-minute thumping, breaking the Canadian's serve at will to race through the next 11 games to move 6-1 5-0 ahead before Bouchard stopped the rot.