The 14th seeded Belarusian - undefeated in 2016, until today's shock loss - was the clear front-runner to challenge world No. 1 Serena Williams for the crown after her stellar start to this year.

But in a chaotic year of upsets in the women's draw, Kerber pulled off another one.

Sensing the game was slipping away from her, Azarenka rallied to capture the double break and lead 5-2 in the second set.

But nerves got the better of Belarusian, who lost the next five games to bow out of the Open in inglorious fashion.

"It was an incredible feeling," Kerber said of the second-set fightback.

"I was more aggressive when it was 2-5, I was telling myself to forget the score, to just play my best," she said.

"It's my first time to the semi-finals here."

Since fighting off a match point against Japan's Misaki Doi in the first round of the tournament, Kerber has not dropped a set on her way to the last four.