Serena Williams, the No. 1 seed at the U.S. Open and regarded as a heavy favorite to win the title, lost to the No. 10 seed Karolina Pliskova in its semifinals Thursday night. The score was 6-2, 7-6. This is the second year in a row that Williams lost in the semifinals of the contest and she was on her way to hitting the record for Grand Slam titles in the Open Era.