( CNN ) -- World number one Caroline Wozniacki made a shock exit from the Rogers Cup in Toronto after losing her second round match to Roberta Vinci 6-4 7-5 Wednesday night . Defending champion Wozniacki looked set to force the match into a third and deciding set after building a 5-1 lead in the second , but her Italian opponent rallied to clinch her first victory against a top-five ranked player . `` I thought I could win today , '' Vinci , 28 , told the WTA Tour 's official web site . `` I knew it would n't be easy , but I thought I could . `` I saw she was making a lot of mistakes , especially in the first set ; then in the second set I was just focusing on every point when I was down , trying to stay aggressive and hit some slice to her forehand when possible . '' Wozniacki first rose to the top of the rankings in October 2010 , but the Dane has yet to capture a grand slam title and admitted world number 22 Vinci had outplayed her on Wednesday . `` Today was definitely not my best match , '' said Wozniacki . `` It was very difficult with the wind but also the way Vinci was playing , I did n't get a chance to really get any rhythm . '' `` She slices the ball . It 's tough to get under it , and then she really goes for it on the forehand . She was getting a lot of balls back , as well . She did better than me . '' Vinci will come up against Serb Ana Ivanovic in the third round , after the 23-year-old 's second round opponent Iveta Benesova was forced to retire in the third set of their encounter . Sixth seed and French Open champion Li Na also benefited from a withdrawal , with Peng Shuai unable to compete due to a hip injury . Wimbledon champion Petra Kvitova battled back from 3-1 down in the first set to clinch her match with Anabel Medina Garrigues 7-6 ( 7-3 ) 6-3 and Serena Williams ' winning streak is up to seven matches after the American beat Germany 's Julia Goerges 6-1 7-6 ( 9-7 ) . Williams , 29 , will now face Zheng Jie , who benefitted from second seed Kim Clijsters ' retirement on Tuesday . Third seed Vera Zvonareva notched up a straight-sets success against Nadia Petrova to set up a third round clash with Poland 's Agnieszka Radwanska , who defeated Croat Petra Martic 6-3 6-3 . Maria Sharapova , who was beaten in the 2011 Wimbledon final by Kvitova , is into the round of 16 courtesy of a 6-1 7-5 triumph against Bojana Jovanovski . Sharapova , seeded fifth , will play Gaina Voskoboeva after the qualifier beat Italian Flavia Pennetta .
Top seed Caroline Wozniacki is out of the Rogers Cup following a defeat to Roberta Vinci . French Open winner Li Na and Wimbledon winner Petra Kvitova win their 2nd rd matches . Maria Sanchez , Serena Williams and Vera Wang also advance in star - group event .