WTA Finals: Williams, Halep enjoy opening wins

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

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 last month and Williams struggled early in an arena hosting the event for a first time.

Pre-match pyrotechnics left the Indoor Stadium looking as hazy as the city-state's streets on a polluted day but once the smoke had cleared, Williams was forced to dig deep in her first service game, staving off two break points before holding.

"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.

"I was fighting as hard as I could and I think I am losing my voice from all of those 'come ons' I was shouting."

The victory was Williams' 16th in a row at the tournament as the 33-year-old American remains on course for a hat-trick of titles as she attempts to retain a number one ranking under threat from Maria Sharapova this week.

Halep continued to hound Bouchard

In the second match, Romania's Simona Halep joined Williams at the top of the Red Group standings after the world number four brushed aside Canada's Eugenie Bouchard 6-2, 6-3 on the purple hardcourt at Singapore's Indoor Stadium.

Bouchard, 20, could barely find the court with her attempted winners as Halep continued to hound her at every opportunity and it was somewhat fitting that a double fault on match point handed victory to the Romanian in just 68 minutes.

"I played really well and am so happy that I was able to find my game again. I stayed aggressive and got plenty of winners but she's a great player, very young and has a big future ahead of her," Halep said.

Ailing Nadal eases into Swiss Indoors 2nd round

Rafael Nadal did not appear to be affected by his appendicitis problems as he charged into the second round of the Swiss Indoors with a no nonsense 6-2, 6-2 win over Simone Bolelli on Monday.

The Spanish second seed has been taking antibiotics to delay the need for surgery and was relieved to emerge unscathed from his match against his Italian opponent.

"I had some doubts that I would be able to compete well," the former world number one told reporters.

"Today was a very positive victory for me. I'm very happy for what happened. With my summer-long wrist injury and now the appendix, it's not been a great season. This was a dangerous match for me and I won it."