Rafael Nadal, the second seed, had it quite a bit easier, advancing when Nicolas Mahut retired with an abdominal strain after falling behind, 6-2, 6-2.  Juan Martín del Potro, who won the title here in 2009 but is on a long comeback from wrist surgery last year, advanced easily through his second-round match against his fellow Argentine Diego Junqueira, 6-2, 6-1, 7-5. He could be headed for a 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 upsets. Sharapova joined a parade of 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.  Sharapova’s undoing was 60 unforced errors, 12 double faults and confidence that visibly seeped out of her as the match progressed.  “Sometimes I come in on a day and I don’t quite have my rhythm and you run into those errors where not only do I feel like I have to get a high percentage of first serves, but my opponent gains a tremendous amount of confidence on their return,” Sharapova said. “So it’s kind of a lose-lose situation.”  The final game, in which Pennetta broke Sharapova’s serve, 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.  “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.”  Pennetta called her victory one of the best matches of her career and said that she too got nervous in the third set.  “I just was trying to focus on my game, trying not to think about the score and anything else, but so many thoughts keep coming into your mind,” she said.  Now Pennetta can start thinking about her fourth-round match against Peng Shuai of China, the 13th seed, who beat No. 19 Julia Goerges of Germany, 6-4, 7-6 (1).  The No. 2 seed, Vera Zvonareva, encountered nothing to get nervous about in her 6-4, 7-5 victory over Anabel Medina Garrigues.  In the men’s draw, del Potro hopes to create a stir after a long, slow crawl back to playing the game that lifted him to No. 4 in the world after he won the Open in 2009. There has been nothing long or slow about his first two matches. Del Potro cruised through his second-round match Friday against Junqueira. In terms of talent, this was not a fair fight, with the smooth and powerful del Potro dictating almost everything.  “I am glad,” del Potro said. “I played better than my first round. I was more confident with my forehand, especially in the beginning of the match, and it is always important to get through.”  At one point in the second set, Junqueira dived for a shot that was well out of his reach and skidded to the court. He got up rubbing his hand and wrist, and del Potro walked to his side of the net to hand him a towel and to ask if he was all right.  Del Potro next will play Gilles Simon, the No. 12 seed.  “It doesn’t matter if you play good or not in the first round if you win,” del Potro said. “Now I’m in the third one, so I need to improve. I need to be more confident with my serves and forehands.”  A version of this article appears in print on September 3, 2011, on Page D1 of the New York edition with the headline: Boldface Name Is Added to Upset List. Order Reprints| Today's Paper|Subscribe
Maria Sharapova, the No. 3 seed and the 2006 Open champion, is the highest seed to fall in the tournament so far.