Williams defeated 11th- seed Flavia Pennetta, 6-3, 6-2, after being broken twice in the first and falling behind 3-1.
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On Friday, Williams will meet Ekaterina Makarova, a Russian seeded 17th who advanced to her first Grand Slam semifinal by eliminating Victoria Azarenka 6-4, 6-2. The other women’s semifinal will be No. 10 Caroline Wozniacki of Denmark against unseeded Peng Shuai of China.
The Associated Press contributed to this report.
