Serena Williams was upset in the US Open semifinals for the second year in a row, beaten 6-2, 7-6 (5) by 10th-seeded Karolina Pliskova of the Czech Republic on Thursday night. Williams, who clutched at her left leg between points in the second set, double-faulted to end it. Afterward, her coach, Patrick Mouratoglou, said Williams injured her left knee in the quarterfinals, the AP reports. The loss prevents Williams from earning her seventh championship at Flushing Meadows and 23rd major title overall, which would both have been Open-era records.
The loss also means Williams' 3 1/2-year reign at No. 1 in the WTA rankings will end. She will be overtaken on Monday by current No. 2 Angelique Kerber, who defeated Caroline Wozniacki in Thursday's second semifinal. In a massive upset last year, Williams' bid for a calendar-year Grand Slam ended when she lost in the US Open semifinals to unseeded Roberta Vinci of Italy in the semifinals. This was the 33rd major semifinal of Williams' career, and the first for Pliskova, 24, who beat the 34-year-old American's older sister, Venus, in the fourth round. Pliskova is only the fourth woman to beat both Williams siblings during the same Grand Slam tournament. (Read more US Open Tennis stories.)