Serena stunned by Pliskova in US Open semis; loses world no.1 ranking

For the second straight year Serena Williams saw her bid for a record seventh US Open title halted in the semi-finals with a 6-2 7-6(5) loss to Karolina Pliskova on Thursday that also ended the American's long reign as world number one.

A year ago Williams arrived at the semi-finals on the cusp of a rare calendar-year grand slam when unseeded Italian Roberta Vinci, a 300-to-1 longshot, recorded one of the biggest upsets in grand slam tennis.

There is no calendar-year grand slam up for grabs this year but history continued to beckon Williams, who would have stood alone as greatest grand slam champion in the professional era if she had claimed a 23rd title and moved past Steffi Graf.

After 186 consecutive weeks as world number one Williams, who had to reach the final to have any chance of retaining top spot, will relinquish the ranking to Germany's Angelique Kerber.

Pliskova will play either second seed Kerber or unseeded Caroline Wozniacki in Saturday's final.