( CNN ) -- 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 could n'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 did n'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 . Read more : Andy Murray to step up comeback . 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 .
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 .