Serena Williams won the Toronto WTA title, her first back-to-back in three years, on Sunday by beating Samantha Stosur from Australia 6-4, 6-2, paving her way to play US Open, which starts in two weeks' time. Williams hammered nine aces and won 89 percent of her first serve points in beating the Australian in straight sets at the 2. 05 million US dollar hardcourt tournament, two weeks after winning the Stanford title. The Roger Cup victory was Williams' 39th of her career and 11th win in 11 matches on the US hardcourt swing this summer. The 29-year-old is currently ranked 80th in the world and was competing in just her fourth tournament since being sidelined for a year by injuries and illness. Her win over Stosur took just 77 minutes as she played six matches in six days in Toronto and served notice that she is returning to form just ahead of the 2011 US Open. Williams broke Stosur's serve to go up 5-4 in the first set. She would break Stosur twice more in the second set before clinching the victory with a blistering ace. Sunday's victory was her biggest since winning her fourth Wimbledon crown in 2010. She was injured shortly after capturing that Wimbledon title, cutting her foot in Germany on a piece of glass and underwent two operations. She then spent 20 weeks in a cast and walking boot. In February, she was diagnosed with blood clots in her lung, and didn't start practising again until April.