Twice champion Azarenka had lost just 11 games in her previous four matches at the tournament but found herself 4-0 down in the first set, which German Kerber went on to take in 48 minutes.

Azarenka mounted a comeback in the second set and had a chance to serve it out at 5-2 but seventh seed Kerber saved three set points, then saved two more in the 10th game to level the set at 5-5.

Kerber kept up the pressure and clinched the match in one hour, 45 minutes. She next faces the winner of the quarter-final between Chinese qualifier Zhang Shuai and unseeded Briton Johanna Konta.

(Reporting by Greg Stutchbury; Editing by Peter Rutherford)