Serena Williams‘ ambition to win three straight U.S. Open championships looked to be coming apart at the start of her quarterfinal match against Italy’s Flavia Pennetta on Wednesday.Williams lost the first three game of the match. But she did not lose her confidence. In fact, she somehow found some optimism in the shaky play.“I don’t feel like I was doing too much wrong,” the five-time champion at the U.S. Open said. “So I said, ‘If she keeps it up, she absolutely deserves the win.’ And I just tried to do a little better.”Well, she did much better. Williams won the next six games to take the set and go on to a relatively pedestrian 6-3, 6-2 conquest to advance to the semis to face 17th-seeded Ekaterina Makarova.Getting to this point was a treat for the best player in the world: She had not reached the semifinals in a major this year. She lost in the fourth round at the Australian Open, the second at the French Open, and the third at Wimbledon. The last time she didn’t reach at least one Grand Slam title match in a season was 2006, when she entered only two of the sport’s top tournaments.“Well, honestly, I’ve had a tough year in the majors and I’ve (lost to) some great players that weren’t in the top 10,” Williams said. “So you can never underestimate anyone.”Williams is bidding to become the first woman with three consecutive U.S. Open titles since Chris Evert won four in a row from 1975-78. The 32-year-old American also is trying to pull even with Evert and Martina Navratilova at 18 Grand Slam singles trophies.