An all-action Serena Williams eased concerns over her injured knee as she opened the WTA Finals with a 6-4, 6-4 victory over Ana Ivanovic on Monday.
The world number one 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.
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, which she said she'd only done once before on court.
"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 number one 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," she added.
Williams recovered from a slow start to earn the first break, but Ivanovic saved break points at 4-1 before a net cord helped her break back and win three games in a row for 4-4.
However, the Serb wasted another break point when she volleyed long and as she served to stay in the set, Williams made her pay when she grabbed her second break and the first set 6-4.
An attritional second set came alive in the seventh game when Ivanovic's baseline smash winner was followed by Williams' fabulous cross-court drop-shot as the American went 4-3 ahead.
With Ivanovic serving at 4-5 down, Williams again raised her game as she drilled a backhand down the line, before converting the first of two match points when the Serb went long.
"You come up against the best, you really have to try and make all parts of your game at that level," Ivanovic said. "That's going to be my big focus for the next matches."
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 number four, 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," she said.