LONDON (AFP) - Ana Ivanovic raced into the fourth round at Wimbledon with a straight sets defeat of Australia's in-form Samantha Stosur on Saturday. The Serbian former world number one beat the 18th seed 7-5, 6-2 in an hour and 10 minutes on the new 4,000-capacity Court 2. The 13th seed now faces defending champion Venus Williams, the third seed, for a place in the quarter-finals. "I played really well and I'm very happy that my tactics and my game plan prevailed over my emotions," said Ivanovic who been match points down in her first round clash against Lucie Hradecka of the Czech Republic. "Grass is such a specific surface, and you really have to understand it to do well. And this is the first year that I feel I'm starting to use grass to my advantage. She played with her right knee taped up but said it was not troubling her. "Still after my matches I have to keep icing it and do some work on it. But it's feeling 100 percent stable. I can practice as normal and play my matches." Stosur, the reigning Wimbledon mixed doubles champion, felt she had chances to win the match. "I didn't play horrible, I thought she played pretty well but at the critical times when I needed to play better I didn't do that," the Australian number one told AFP. "I gave her two breaks of serve, which she didn't really have to work too hard for, and on grass that's all you need. "Once I got back to 5-4 I thought I was definitely back in the match and could have had the chance to win the first set. "I never built on that lead. That's what's disappointing because I got myself back in it and gave it away straight away." Ivanovic, the 2007 Wimbledon semi-finalist, broke early but failed to put the pressure on and could have lost the set. She lost her serve at 4-3 up and Stosur, a surprise semi-finalist at the French Open, held serve to leave Ivanovic serving to stay in the set. She held her serve and took a 6-5 lead when Stosur double-faulted. Ivanovic then won the set with two set points to spare when Stosur sent a backhand into the net. Though Stosur was serving slightly faster than the Serbian number two, Ivanovic was getting more first serves on target and converting far more points on her first serve. Ivanovic broke in the first game of the second set and raced into a 5-1 lead. She missed a match point at 5-1 as though Stosur held on to make it 5-2, Ivanovic won the next game to progress to the fourth round.