Defending champion Angelique Kerber bowed out in the Australian Open fourth round after being blown away by American Coco Vandeweghe.
Kerber was the second number one seed to crash out on a day of shocks in Melbourne after Andy Murray had earlier been beaten in the men's tournament by German Mischa Zverev.
Vandeweghe was a worthy winner too on Rod Laver Arena, winning 6-2 6-3 in just 68 minutes to book a quarter-final showdown with Garbine Muguruza.
Ranked 35th in the world, the American lost in the first round here 12 months ago, just as Kerber was beginning her path to become champion.
The world number one, however, has endured a difficult start to 2017 and her fragile confidence was ruthlessly exposed here by a powerful display of baseline hitting.
"It was really special," Vandeweghe said. "Beating the world number one on any stage and any place is great... I'll take this one.
"I wasn't feeling confident, I guess I faked it. I was nervous, but I had a game plan to execute and I knew that as along as I keep picking my spots, I had a chance."