After her 7-5, 6-1 defeat to Serena Williams in the Stanford final, France’s Marion Bartoli says that the American is already one of the U.S. Open favorites.

"She has really improved her level from Wimbledon," said Bartoli, who had taken down Serena at Wimbledon. "She beat [Maria] Sharapova and [Sabine] Lisicki easily [at Stanford] and everything is just better, her serve, her movement. I would pick Serena [as the US Open favorite] considering how many times she won there. Six weeks from now, she’ll be more than 10 percent better."

Bartoli added that three-time U.S. Open champion Kim Clijsters cannot be considered a favorite yet. Clijsters pulled out of next week's tournament is San Diego, but is scheduled to return in Toronto.

"Kim hasn’t played match for a long time and when she played Roland Garros she was far from her best level,"  Bartoli said. "We have to see how she shows up in Toronto and Cincinnati. It's hard to put her as favorite because she hasn't done too much since the winning the Australian Open."