Pliskova came from 5-1 down in the final set and saved four match points to claim a stunning 6-4 4-6 7-5 victory in the quarter-final on Rod Laver Arena.

Williams appeared to be in complete control until she rolled her ankle in the seventh game of the final set and Pliskova took advantage.

The Czech seventh seed moved into a third major semi-final, where she will face Japanese star Naomi Osaka.

Williams was eyeing an eighth title in Melbourne and 24th grand slam crown – to go level with Margaret Court – but Pliskova produced the huge comeback.

Both players made a clean start before Pliskova landed the first blow of the contest, breaking in the third game.

A backhand winner down the line set up break point, converted when Williams put a backhand into the net.

Williams had seemed to be reluctant to miss her first serve, with her speeds well down early compared to previously this tournament.

She picked it up in the fifth game, but had to fight her way out of a 0-40 hole and fend off four break points to hold serve.

Pliskova, who had her left knee taped, was in fine form throughout the opening set, closing it out with an ace.

The first chance to break in the second set went to Pliskova, who struck when Williams sent a backhand into the net in the fifth game.

But Williams responded immediately and broke once more at the perfect moment in the 10th game to take the second set 6-4.

Seemingly with all the momentum, Williams started to take control, breaking for 3-1 in the third set with a wonderful cross-court forehand return winner.

Williams rolled her left ankle while serving at 5-1 – a match point also going begging – and Pliskova incredibly got back on serve.

Pliskova was forced to save three more match points in an enthralling 10th game, a backhand winner making it 5-5.

The Czech broke Williams to love in the next game and then sealed the amazing victory when her opponent sent a forehand into the net on match point.