Serena Williams’ hopes of a record-equaling 24th Grand Slam singles title was quashed as she lost to a one time regular opponent in Victoria Azarenka, their first encounter in the latter stages of a Grand Slam since a Wimbledon quarter-final in 2015.
The American, who was aiming to equal the all-time record for majors, started brightly by winning the first set but lost 1-6 6-3 6-3 to the spirited former world number one.
The American beckoned on her trainer early in the third set after suffering an Achilles problem and struggled physically from then.
Two-time Australian Open champion Azarenka has been extremely good in recent weeks, having now won 11 matches in a row after victory in the Western & Southern Open just before the US Open.
The match against Williams was her first Grand Slam semi-final since 2013 after troubled times on and off the court.
The Belarusian faces Japan’s 2018 champion Naomi Osaka in the final.
Osaka defeated Jennifer Brady 7-6 (7-1) 3-6 6-3 to book a spot in the final.