Serena Williams shook off the rust and a feisty challenge from Serbia's Ana Ivanovic to open the defence of her WTA Tour Finals title with a 6-4, 6-4 victory in the opening match of the elite eight-player tournament.

Williams came into the finals after injuries forced her out of her previous two outings and following Russian official Shamil Tarpischev's disparaging comments about her and sister Venus.

Illness and a knee problem forced the American world number one to withdraw from her last two tournaments since winning a third straight US Open title at the start of September and Williams struggled early on the purple hard court in Singapore.

"I am really excited with how I played tonight. I have been working hard all my life for nights like this and I love it. So thank you for coming tonight," Williams at a courtside.

The victory was Williams' 16th in a row in the tournament closing in on Martina Navratilova's record of 21 straight wins at the season-ending tournament.

Later, Romania's Simona Halep comfortably defeated Canada's Eugenie Bouchard 6-2, 6-3.

In a clash of the only two players making their first appearance at the season-ending championships, Halep lost only four points when getting her first serve into play.

Bouchard was well below her best, racking up 30 unforced errors against 11 from Halep.

In Tuesday's White Group matches, Maria Sharapova takes on Caroline Wozniacki and Petra Kvitova faces Agnieszka Radwanska.

Source: Agencies