An all-action Serena Williams has eased concerns over her injured knee as she opened the WTA Finals with a 6-4 6-4 victory over Ana Ivanovic.
The world No.1 withdrew from this month's China Open with a left knee problem but she showed no discomfort during an entertaining round robin win in Singapore on Monday.
With no strapping on her knee, Williams slid around the court and at one point did the splits. She shouted "Come on!" so many times she made herself hoarse.
"I never do it in practice," said Williams of her impromptu splits in the final game.
"I never run that hard in practice. I save it for a match. I do work on my flexibility, but not for tennis. Because I dance... I guess it comes in handy."
After a nervy start it was an ultimately convincing win from the top seed, who is seeking her third straight season finale victory and the year-end world No.1 ranking.
Later in the eight-player tournament, Romania's Simona Halep enjoyed a straightforward 6-2 6-3 victory over a misfiring Eugenie Bouchard of Canada.
Williams also pulled out of last month's Wuhan Open with illness and the American said she felt like she had "nothing to lose" as she totted up her 16th straight WTA Finals win.
"I didn't have any fear at all. I felt pretty good. I really felt like I don't really have anything to lose at this point," she said.
"I felt the knee a little bit, but compared to what it was in Beijing, it feels so much better. I'm getting better, which is great."
Williams' victory puts her in the box seat for a place in the semi-finals with Red Group matches still to come against Halep and Bouchard, the tournament's youngest players.
Halep, the world No.4, gave Bouchard a miserable introduction to the elite event as she broke twice in each set and profited from the Canadian's 30 unforced errors.
"I played really well, I'm really happy I found my game again," said Halep, who will face Williams in her next match.
"Of course she's the best player in the world and I have nothing to lose. I'll try to play my game and to fight for every point."
