The 10th seed Karolina Pliskova outplayed Serena Williams and will face Angelique Kerber in US Open final
Williams the 34 year old American double-faulted on match point to lose 6-2 7-6 (7-5) and ended her reign as world number one.
The defeat ascertained that Kerber will overtake Williams at the top of the rankings after the US Open.
Williams has also dented her hopes to win an Open-era record 23rd major singles title.
She remains tied with Steffi Graf for both Grand Slam titles, and the WTA record of 186 successive weeks as world number one.
This is a huge moment of joy for Karolina Pliskova as she had never been past the third round of a Grand Slam before this week.
“Karolina played great today,” said Williams after the match.
“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”,she added.