US Open: Serena Williams defeated by Karolina Pliskova, loses No.1 ranking

Serena Williams was defeated at the U.S. Open semi-finals stage by Czech player Karolina Pliskova, 6-2, 7-6 on Thursday night September 8 at the USTA Billie Jean King National Tennis Center in New York City.

''I don't think much really went well today,'' Williams said. ''I made a lot of errors and I didn't play as well as I have been playing. I have been having some serious left knee problems. I wasn't tired. Fatigue had absolutely nothing to do with it. If I was tired I should definitely get into a new career. I wasn't able to move the way I wanted to move. When you're injured you're thinking of other things when you should be just playing and thinking of your shots. My mind was just a little bit everywhere. But it was what it was.''

This marks the second consecutive year that the 34-year-old tennis player has dropped out of the US Open in the semifinal round.

Serena has been ranked number one for 186 weeks and when the new rankings are released on Monday, Angelique Kerber will land in the top spot, according to reports.