Serena Williams' latest bid for a 24th Grand Slam singles title ended as Victoria Azarenka rolled back the years to reach the US Open final.

Williams, seeking to equal the all-time record for majors, raced away with the first set but lost 1-6 6-3 6-3 to the inspired former world number one.

The American called on the trainer for an Achilles problem early in the third set and struggled physically from then.

Belarusian Azarenka faces Japan's 2018 champion Naomi Osaka in the final.

Two-time Australian Open champion Azarenka had been appearing in her first Grand Slam semi-final since 2013 after troubled times on and off the court.

But she has been in fantastic form in recent weeks, having now won 11 matches in a row after victory in the Western & Southern Open just before the US Open.