Germany's Angelique Kerber makes a backhand return to United States' Coco Vandeweghe during their fourth round match at the Australian Open in Melbourne, Australia, on Jan 22, 2017. [Photo/IC]

The top half of the women's draw is open, too. Venus Williams returned to the quarterfinals for the ninth time with a 6-3, 7-5 win over No. 181-ranked Mona Barthel.

The seven-time major winner next plays No. 24-seeded Anastasia Pavlyuchenkova, who beat No. 8 Svetlana Kuznetsova 6-3, 6-3.

Muguruza beat Sorana Cirstea 6-2, 6-3 and will next play Vandeweghe — they're both in the quarterfinals here for the first time.

Kerber's loss continued a poor run since she won the US Open last September. She's played seven tournaments without winning a title, only reached one final, and was 5-7 against top-50 players.

The bigger upset of the day, then, was produced by Zverev, the older and apparently lesser-talented brother of Alexander who had never gone past the third round of a major and was appearing at only his third Grand Slam in six years.

Zverev attacked Murray, unsettling his natural baseline game, and won 65 of 118 points at the net. Murray had reached the quarterfinals or better on his previous seven trips to Australia but never won the title.

He had not lost to a player ranked as low as Zverev at a major since his loss to No. 51 Juan Ignacio Chela here in 2006.

Zverev next plays Federer, who beat him 6-0, 6-0 in 40 minutes in their last meeting in 2015.

He made some stunning, lunging volleys on clutch points against Murray, but for him it was all a blur.

"It was like I was in a little coma, I just served and volleyed my way through," Zverev said. "Honestly there were a few points where I don't know how I pulled it off."