(CNN) -- After Roger Federer's escape in the men's quarterfinals, there was yet more drama at the U.S. Open in Friday's women's semifinals. But the scenes inside Arthur Ashe Stadium in New York weren't as riveting as the Swiss' comeback from two match points and two sets down against Gael Monfils on Thursday. Whereas Federer walked off court as the winner, a teary Peng Shuai had to be taken off the court in a wheelchair moments after crumpling to the ground with what tournament organizers called a heat-related illness. Trailing 7-6 4-3, China's Peng -- in her maiden grand slam singles semifinal -- retired and it gave Denmark's Caroline Wozniacki a place in the final against Serena Williams.
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Caroline Wozniacki faces Serena Williams in the U.S. Open final
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Wozniacki advances in dramatic fashion after her opponent retired
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China's Peng Shuai had to be taken off center court in a wheelchair
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World No. 1 Williams crushed Russia's Ekaterina Makarova in an hour
1 Wozniacki likely earned more backers when she crossed the net to check on the stricken @placeholder.