Shock defeat for Serena Williams in US Open - loses number one ranking to Kerber

Williams will hand over the number one ranking to Kerber at the end of the tournament

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).