Sharapova, the No. 3 seed and the 2006 Open champion, is the highest seed to fall in the tournament so far.
Rafael Nadal, the second seed, advanced when Nicolas Mahut retired after falling behind, 6-2, 6-2.
Juan Martin del Potro, who won the title in 2009 but is on a long comeback from wrist surgery last year, advanced easily through his second-round match with fellow Argentine Diego Junqueira, 6-2, 6-1, 7-5. He could be headed for a big fourth-round clash with John Isner, seeded 28th, who overpowered Robby Ginepri, 6-4, 6-3, 6-4.
So far, it is the women’s draw that is pockmarked with crazy upsets. Sharapova joined a parade of frustrated women who entered the tournament with low numbers next to their names only to find their stays shortened in unlikely fashion. Already gone are No. 5 Petra Kvitova, who beat Sharapova in the Wimbledon final, No. 6 Li Na, and No. 8 Marion Bartoli.
For Sharapova, the undoing was 60 unforced errors, 12 double faults, and confidence that visibly seeped out of her as the match progressed. She lost four break points while trailing, 2-0, in the third set.
Sharapova was largely considered the biggest remaining threat to No. 28 Serena Williams, but now the Russian is gone, as well.
“It’s disappointing to lose in the middle of nowhere, disappointing to lose in New York,’’ Sharapova said. “Losing isn’t fun for anyone because we work to win. We don’t work to lose.’’
The final game, in which Pennetta broke Sharapova’s serve to win, was a microcosm of the match. Sharapova started with two double faults, then Pennetta pounced on her next two tentative serves. She ripped a backhand service return for a winner on match point to complete her victory.
The loss was Sharapova’s first in 13 three-set matches this year.
“She’s a good fighter, you know,’’ Pennetta said. “You can never give up with her. You have to be focused until the last game, until the last point, actually.
“But I think at 5-4 she’s starting to feel a little bit of pressure, also. She has a lot of double faults. But during this season also she played really good, she had good results, but also with the serve she isn’t serving like before. So I think she is just feeling the pressure.’’
