Rome, September 5 - Flavia Pennetta will face second seed Victoria Azarenka in her first grand slam semi-final after thrashing Roberta Vinci 6-4 6-1 in an all-Italian 'derby' in the last eight of the US Open. The result certifies the return to form of Pennetta, who was the first Italian woman to reach the top 10 of the WTA rankings in 2009, but who dropped outside the top 150 after having wrist surgery last season. The 31-year has not dropped a set on her way to the last four at Flushing Meadows. As well as beating 10th seed Vinci, she also turfed out her fourth-seeded compatriot Errani in the second round. "I'm proud of myself now," said Pennetta. "I'm 31, and physically I feel good at last. I'm in my first semi-final in a grand slam".