- Serena Williams starts defense of WTA Championship title with win over Angelique Kerber
- World No.2 Victoria Azarenka also a winner on Tuesday beating Sara Errani 7-6, 6-2
- Stanislas Wawrinka crashes out of home ATP Tour 500 event in Basel, Switzerland
Defending champion Serena Williams breezed past Germany's Angelique Kerber in her opening match at the WTA Championships in Istanbul's Sinan Erdem Dome on Tuesday.
The world No.1 needed just 65 minutes to overpower the World No.9 winning 6-3, 6-1 as she looks to seal a fourth WTA Championships crown and an incredible 11th title this season.
"I feel really good -- I think I served very well -- and she's beaten me before so I was just a little nervous and so focused going into this match. I felt like I was going to have to play well to win," Williams said.
"I'm actually happy about my match and I never say that! I'm really excited about that. I've been working really hard since the Open and hopefully I can continue with that here."
Earlier, World No.2 Victoria Azarenka was made to work a little harder against Sara Errani.
The Belarusian eventually came thorough 7-6, 6-2 but only after her Italian opponent sustained a calf injury at the start of the second set.
Errani battled bravely but couldn't stop Azarenka bringing an end to a three-match losing streak which began at the U.S. Open final where she lost to Williams. That defeat was followed by consecutive first round exits at events in Tokyo, where she lost to sister Venus before she was dumped out in the first round of the China Open in Beijing by Germany's Andrea Petkovic.
"I was missing a little bit too much at the beginning but I turned it around," Azarenka said after beating Errani.
"It was a little bit difficult to focus in the second set because I didn't know what was going on (with Errani's injury). Even after the time-out, she was returning unbelievably and fought until the last point."
Sixth seed Petra Kvitova had a good head-to-head record going into her match against Poland's Agnieszka Radwanska and once again came out on top.
The Czech triumphed in straight sets 6-4, 6-4 to improve her match record against the World No.4 to 5-1 and secure her 50th win in a WTA match this year.
The season finale features the top eight singles players and the top four doubles pairings who are competing for a $6 million prize pot.
Wawrinka crashes out in Basel
Two ATP Tour 500 events are taking place this week as the top men look to secure their place at the season-ending World Tour Finals at the O2 Arena in London which start on November 4.
Home favorite Stanislas Wawrinka crashed out in the first round of the World Tour 500 event in Basel, Switzerland going down in straight sets 6-4, 6-3 to Edouard Roger-Vasselin of France.
The Swiss No.2 is currently eighth in the rankings, but seventh in the Race to London given that Andy Murray has withdrawn from the event. Wawrinka can secure his place at the London finals with a good showing at the Paris Masters next week.
Tomas Berdych also suffered a shock defeat at the hands of Croatian Ivo Karlovic. The 34-year-old veteran dispatched the World No.6 4-6, 7-6, 7-6.
Berdych would have guaranteed a place at the World Tour Finals in London if he had reached the semifinals in Basel, but will now have wait until next week to seal a top eight slot.
Elsewhere, there were comfortable wins for Cypriot Marcos Baghdatis who overcame Germany's Benjamin Becker 7-6, 6-1, and Croatia's Ivan Dodig, who is through to the second round after his opponent Carlos Berlocq retired after two games.
Meanwhile at the ATP Tour event in Valencia, Spain's Nicolas Almagro is safely through to the second round after beating compatriot Pablo Andujar 6-2, 6-3.
But there was disappointment for the Spanish crowd as Fernando Verdasco went down 6-3 7-6 to Polish qualifier Michal Przysiezny and Feliciano Lopez lost out 6-3, 6-1 to France's Julien Benneteau.
Przysiezny's compatriot Jerzy Janowicz also overcame Spanish opposition defeating Pablo Carreno 7-5, 7-6.
Russia's Mikhail Youzhny is through to the second round after Bernard Tomic retired. The Australian pulled out of the match when he was trailing 4-1 in the final set.