Williams won her opening match at the WTA Finals on Monday, beating Ana Ivanovic 6-4, 6-4 in the Red Group for her 16th consecutive victory at the season-ending tournament in Singapore.

Williams came into the finals after injuries forced her out of her previous two outings.

The top-ranked Williams was shaky in her opening service game, saving two break points, but still took a 4-1 lead.

The Serb got back on serve but lost the first set when she double-faulted at 15-40 in the final game - one of her seven double faults.

Ivanovic broke Williams to open the second set but the American immediately broke back and took control, improving her career record against the Serb to 8-1.

Before the WTA Finals, Williams retired from the China Open and Wuhan Open because of illness and a left knee injury that had her in doubt for Singapore.

With the win over Ivanovic, she closed in on Martina Navratilovaâ€Ös record of 21 straight wins at the season-ending tournament. (KH)