SINGAPORE (AP) — With no injuries to slow her down, Serena Williams extended her winning streak at the WTA Finals to 16 straight matches with a 6-4, 6-4 victory over Ana Ivanovic on Monday.

The top-ranked Williams came into the season-ending tournament after injuries forced her out of her previous two tournaments and with the off-court distraction of disparaging comments about her from Russian tennis official Shamil Tarpischev.

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. But with the win over Ivanovic, she closed in on Martina Navratilova’s record of 21 straight wins at the tournament.

“I just found out last time that I was 15 matches and I was like, ‘Oh boy, not another streak,'” Williams said. “So now I’m 16 and, gosh, here we go again.”

In the other Red Group match, Simona Halep beat Eugenie Bouchard 6-2, 6-3 in a meeting between the only two newcomers in the eight-player field.

On Tuesday in the White Group, Maria Sharapova will take on Caroline Wozniacki and Petra Kvitova will face Agnieszka Radwanska.