Serena Williams loses number one world ranking after shock US Open defeat
Serena Williams admits her pursuit of a record-breaking 23rd grand slam title was hampered by a knee injury after she crashed out of the US Open to Karolina Pliskova.
Williams was bidding to surpass Steffi Graf's Open-era record 22 major triumphs but she bowed out in Arthur Ashe Stadium to a ruthless Pliskova, who won 6-2 7-6 (7/5).
The top seed's disappointment is doubled as she also surrenders the world number one ranking to Angelique Kerber.
Pliskova will meet Kerber in Saturday's final at Flushing Meadows after the German overcame Caroline Wozniacki 6-4 6-3 in the other semi-final.
It is the second year running Williams has lost here in the semis and the 34-year-old, who turns 35 later this month, was hobbling in the second set.
After the match, she revealed she had been nursing a problem with her left knee in New York since round two.
"Yeah, I have been having some serious left knee problems," Williams said.
"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."
Williams was reluctant to discuss how long the injury might affect her and the rest of her schedule this year but was adamant she was not affected by fatigue.
While Pliskova cruised through her quarter-final against Croatia's Ana Konjuh on Wednesday, Williams was made to work hard by fifth seed Simona Halep, before winning in three sets.
"I wasn't tired from yesterday's match," Williams said. "I'm a professional player and have been playing for over 20 years.
"If I can't turn around after 24 hours and play again then I shouldn't be on tour. So I definitely wasn't tired from yesterday's match at all."
Williams added she is used to playing matches on back-to-back days given it is commonplace at most events outside the grand slams.
"I don't see how it's not fair," Williams said. "We play every single week. I have been in Toronto or Montreal or Cincinnati where I play Wednesday, Thursday, Friday, Saturday, Sunday.
"If I'm not used to playing this much then I really should think of something different. I'm not going to sit here and make an excuse."
Williams will hand over the number one ranking to Kerber at the end of the tournament and subsequently fails to break another record of Graf's.
Graf and Williams had both spent an unmatched 186 consecutive weeks at the top but the American refused to discuss the matter. "I don't talk about that whatsoever," she said.
Williams did give a nod of appreciation to Pliskova, who outgunned her opponent at her own game, with power, aggression and a blistering serve.
Pliskova delivered seven aces to her opponent's six, won 84 per cent of points on her first serve and gave away just one break point.
"Karolina played great today," Williams said. "I think if she had played any less then maybe I would have had a chance.
"So I think I wasn't at 100%, but I also think she played well. She deserved to win today. I thought she served well and that was definitely a big thing for her."