There will not be a record 188 weeks as No.1 for Serena Williams as the American was – for the second year running – knocked out of the US Open in the semi finals.

After battling through in three sets against Simona Halep in the quarters, there was no hiding place against 10th seeded Karolina Pliskova on Thursday night at the Arthur Ashe Stadium.

The 24-year-old Czech continued her hard-hitting, beating Serena 6-2, 7-6 before a largely partisan crowd.

And in the second semifinal, Angelique Kerber defeated former No.1, Caroline Wozniacki, 6-4 6-3 to make it to her third Grand Slam final of 2016, having won the Australian Open by defeating Serena Williams.

Kerber is now World number one dethroning Serena.

In 2015, Serena faltered in this same semi final to Roberta Vinci with a chance to win a calendar Grand Slam. This year she was chasing a new record of being No.1 for 188 weeks having equalled Stefi Graf’s 187 weeks as No.1. She was also chasing a 23rd Grand Slam title that would have taken her beyond Graf.

Serena later disclosed that she had been playing with a serious knee injury that curtailed her movement on court.

“Fatigue had nothing to do with,” Williams said. “Being a professional, if I am not able to recover, I am not going to make excuses.”

She added that she “was not 100 per cent.”

“My mind was elsewhere, you are thinking of other things. I was making errors on simple and simple shots, just blame that on thinking on my leg,” she added.

Serena had needed to make the final and beat Kerber if she was to retain her World No.1 status. But that was always going to be hard in a year in which she has played only seven tournaments.