Serena Williams's three-and-a-half year reign as world No 1 will come to an end after she suffered a shock straight-sets defeat in New York against Karolina Pliskova.

The new head of the rankings is Angelique Kerber, who will face Pliskova in the final after beating Caroline Wozniacki.
While Pliskova smacked down some heavy serves during her 6-2, 7-6 victory, and also struck the ball cleanly off the ground, it is also true that Williams was sluggish and inconsistent throughout. The explanation emerged during her post-match press conference, when she revealed that she had been struggling physically.

“I have been having some serious left knee problems,” said Williams. When asked what effect this had on her game, she replied “Mental, because when you're hampered you're thinking of other things. Like I was making errors that I never make, and definitely I didn't make in this tournament in particular. So many simple, simple shots that I easily could have made. I just blame that on thinking about my leg and just not thinking about the shot.”image

Williams has thus been halted on 186 consecutive weeks at No 1 – exactly the same length of time that Steffi Graf held the top spot for between August 1987 and March 1991. And these two champions also remain tied on 22 grand-slam titles each, for the moment at least.

Williams has now lost in the semi-finals of the US Open in two consecutive seasons, after last year’s even more unexpected defeat at the hands of Roberta Vinci.