ISTANBUL, Turkey -- Top-ranked Serena Williams overcame Agnieszka Radwanska 6-2, 6-4 for her second win in two matches at the WTA Championships on Wednesday and all but sealed a spot in the semifinals. Jelena Jankovic topped second-ranked Victoria Azarenka 6-4, 6-3 in her first match at the tournament and fourth-seeded Li Na opened her campaign with a 6-3, 7-6 (5) victory over Sara Errani. Williams cruised in the first set but ran into some trouble in the second against a player she had never lost to in seven previous matches. "She definitely played pretty well. But, you know, I can always look to improve on some things. My serve wasnt as good today as it was yesterday, but you cant expect it to be great every day," Williams said. Radwanska wasted three break points at the start of the set and dropped her serve in the fourth game. She broke right back and levelled at 3-3, but Williams pounced on her serve again in the final game, winning the match with a backhand winner. Radwanska has won just one set of 17 she has played against Williams overall - in the 2012 Wimledon final. She has now dropped both round-robin matches in Istanbul, where she also lost to Williams in last years semifinals. Williams is bidding for her fourth title in the event. Errani also lost her opening group match on Tuesday to Azarenka and now looks all but certain to be eliminated. Jankovic, who was ranked No. 1 in 2008 and is back in the top 10 for the first time since 2011, outplayed Azeranka to snap a four-match losing streak against a fellow former No. 1. "Vika is a great champion, and I knew it was going to be a tough match. We played against each other in Cincinnati and I lost in three sets, and I think the difference today was that I was serving much better," Jankovic said. Williams, 32, is enjoying the finest season in her career, having already won 10 titles. She added the French Open and U.S. Open titles to bring her Grand Slam record to 17 championships and is 75-4 for the year. Williams, making her eighth appearance in the event, is looking to become the first player to successfully defend the title since Justine Henin in 2007. Henin was also the last to win 10 titles in a season, in 2007. Williams has clinched the year-end No. 1 ranking for the third time in her career after 2002 and 2009 Li trailed 3-1 in the second set against Errani, but won the next four games. She twice attempted to serve for the match, first, wasting a match point at 5-3 and then again at 6-5. Despite trailing 3-1 in the tiebreaker, Li won the next five points and eventually converted her third match point when Errani sent a forehand into the net. That saw her take her head-to-head meetings against her Errani up to six wins without defeat. "The first match is always tight," Li said, adding that she had felt rusty after a three-week break since her last tournament. "I still have to find the rhythm on the court." The tournament brings together the top eight players in the world. They play two round-robin groups, with the top two finishers in each advancing to the semifinals. Jankovic, now ranked No. 8 and seeded seventh because third-ranked Maria Sharapova pulled out of the event with a shoulder injury, proved to be the steadier player against Azarenka, the Australian Open champion. "I was able to hold my serve and stay focused when I was serving and I waited for my chances to break, and she made some double faults at times and I took advantage of that," Jankovic said. "Its a great win for me, it gave me a lot of confidence." The key game in the first set went to Jankovic after more than 10 minutes when she held serve for a 5-3 lead. Azarenka saved two set points in the next game but then sent a forehand wide on Jankovics fourth in the 10th game. Azarenka dropped her serve in the third game to fall behind and then held in the fifth despite serving three double-faults and facing four break points. But she could not trouble Jankovic on her serve and another forehand by Azarenka that sailed long to hand Jankovic the match. "Of course she was playing well. I mean, I think shes playing her best tennis right now. Really improved a lot throughout the year, " Azarenka said. "But I cannot say that I played well and she was better today. Of course she was better today, but, you know, I let a lot of balls go. There were a lot of mistakes, small mistakes, a little bit bigger mistakes." After losing the U.S. Open final to Serena Williams, Azarenka lost her opening matches in both Tokyo and Beijing before beating Errani on Tuesday. Azarenka still has a 5-4 career edge over Jankovic. 16:56ET 23-10-13 Trevor Siemian Vikings Jersey . - The infectious smile was missing from Nam Nguyen last week. Jalyn Holmes Vikings Jersey . Chan captured two silver medals at last months Sochi Winter Games — mens singles and the inaugural team event. But he doesnt have the urge to resume training to defend his world title when the event is held in Saitama, Japan, later this month. http://www.shopvikingsauthentic.com/Youth-Mike-Remmers-Elite-Jersey/ . -- Zach Johnson is like most players at the World Challenge, not sure whether hes still playing in 2013 or if hes in the middle of the new wraparound season that officially started in October. Brian ONeill Jersey . These days, just about anyone can get a taste of the friendship that has blossomed between All-Star Kevin Durant and Oklahoma City Thunder teammate James Harden, most famous in the past two weeks or so for the elbow to the head he took from the Los Angeles Lakers Metta World Peace. Kirk Cousins Vikings Jersey . General manager David Poile called signing Ribeiro a great opportunity to add a talented, experienced and creative centre Tuesday when he introduced the veteran at a news conference. Ribeiros contract is worth $1.05 million after being bought out of the final three years of a $22 million contract by the Coyotes recently. VANCOUVER -- His career was built on making the right choices so its no surprise Jay DeMerit knew the time had come to walk away from playing professional soccer. DeMerit, the first player signed by the expansion Vancouver Whitecaps in 2010 and the Major League Soccer teams first captain, officially announced his retirement Thursday. "When it makes sense, when its right, its not sad," the amiable DeMerit said during a news conference. "Its not something I am going to regret. "Its something I am very proud of." Being convinced he made the right decision didnt stop DeMerit from battling back tears at one point. He will continue to work with the Whitecaps as an ambassador but has other business interests in Vancouver. "I am excited for the future," he said. "By no means is this the end." Known for strong defensive and leadership skills, the centre back had a goal and one assist in 71 career games -- 69 of which he started -- with the Whitecaps. He logged a total of 5,928 minutes during his MLS career. DeMerit spent six seasons with English club Watford FC before joining the Whitecaps. The 34-year-old American also appeared in 25 games with the U.S. national squad, starting four matches at the 2010 World Cup. Two injuries in a 15-month span hobbled DeMerit. In 2013, he missed most of the year with a torn Achilles tendon suffered in the season opener against Toronto FC. Last month, he tore a tendon in his left ankle in a 3-3 draw with the Philadelphia Union. "I knew I was up against it," DeMerit said. It was one day last week while watching the team practise that DeMerit began to question if he could return. "Watching the guys play it just kind of dawned on me I think these days are over," he said. "I looked down and saw an ankle with one real tendon. "I didnt think I had it in me anymore." Later that day while sitting on a Vancouver beach, DeMerit decided to call it a career. "I sat down on a log," he said. "At that exact second, after no other thought, I decided I was going to retire." In a letter to fans posted on the Whitecaps website, DeMerit said if he continued to play he risked damaging the reputation he spent years building. "Ive always been the kind of player who wears his heart on his sleeve and its that heart thats telling me its time to stop," he said. "If I cant be the player that I have always been, and play to a standard that I believe is high enough, then its time for me to smile, say thank you and give my commitment to a new cause." Vancouver president Bob Lenardduzzi said DeMerits charm and charisma off the field played an important role in helping to raise soccers profile in a market dominated by hockey and football.dddddddddddd "Jay gets the big picture," said Lenarduzzi. "He gets that in North America we are selling the sport." DeMerit has made over 120 appearances on behalf of the Whitecaps. "His willingness to participate in virtually any request we put in front of him has helped to strengthen our brand in the market place," said Lenarduzzi. Coach Carl Robinson said DeMerits competitive spirit helped mould the team. "Hes a sore loser," said Robinson. "Hes a pain in the backside sometimes when it comes to training because he wants to win so much. "He leads by example. Young players knew what was expected of them. If they stepped out of line, or didnt do the job properly, he would tell them." DeMerit played college soccer at the University of Illinois-Chicago but was overlooked by pro scouts. He travelled to London with $1,200 in his pocket to pursue a soccer career. In his letter he talked about being broke, "sharing bath water" with a friend and playing games with "nothing but a couple of cows and five people in the stands." Eventually DeMerit would score the goal that sent Watford to the Premiership. He played in an FA Cup semifinal against Manchester United and a League Cup semifinal against Liverpool. He also played on the MLS all-star team that beat Chelsea. In Vancouver he helped the Whitecaps become the first Canadian team to reach the MLS playoffs. The chance to be part of a new franchise appealed to DeMerit. "I thought it was an amazing opportunity to be part of a blank canvas," he said. "Vancouver gave me that opportunity." Playing in Vancouver also allowed DeMerit to meet his future wife, Olympic gold medallist skier Ashleigh McIvor. The couple were married last summer. In his letter, DeMerit talked about what soccer gave him. "I got to travel around the world, grace a few magazines and billboards, and got to see the soccer community come together and raise money to make a movie about my life," he said. "I got to talk about my beloved Green Bay Packers with Elton John while in my underwear and drink beers with Bill Clinton. "I got to meet other amazing athletes and even got to marry the most beautiful Olympic gold medallist on the planet." With one chapter of his life finished, DeMerit is anxious to see what the future holds. "This isnt a career ender," he said. "Its a life starter." 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