Task: Question Answering
Input (English): Passage: Petrova was seeded 18th at the 2010 Rogers Cup in Montreal and won a tough opener against Lucie Šafářová. In the second round, she faced former world No. 1 Dinara Safina and despite serving 15 aces, she was defeated, 7-5, 4-6, 6-4. Petrova played the final event of the US Open Series in New Havan at the 2010 Pilot Pen Tennis, where she received a wild card to play as the eighth seed. In the first round, she came from a set down to beat Varvara Lepchenko. She then defeated her former doubles partner Bethanie Mattek-Sands to advance to the quarterfinals. She then had an impressive 6-2, 6-1 victory over second seed Samantha Stosur for her fourth top 10 win of the season. She defeated Maria Kirilenko in her semifinal match, but was beaten by Caroline Wozniacki in the final, 6-3, 3-6, 6-3. 
Question: How many more points did Petrova score than Samantha Stosur in their match? 
Answer type: Number 
Output (English): 9.