World number ones Andy Murray and Angelique Kerber crashed out of the Australian Open Tennis. 35-year old Roger Federer, however, fought his way closer to an 18th Grand Slam title with a five-set win over Kei Nishikori in the fourth round. The Swiss won the last of his record 17 Slam titles in 2012. Murray was stunned by 50th-ranked serve-and-volley specialist Mischa Zverev in four sets before Kerber, the women's title-holder, tamely succumbed to unseeded American Coco Vandeweghe. The unpredictable results, following six-time champion Novak Djokovic's stunning loss in the second round, opened the door to a host of challengers – with Federer leading the charge. Federer, who looks back to full fitness after a six-month injury lay-off, said the hard-fought, fourth-round win could be significant as he now eyes a quarter-final with Zverev. Murray had been the hot favourite after Djokovic's shock exit, but the Briton lost to Germany's Zverev to extend his wait for a first Melbourne title. For Murray, it was his earliest Melbourne departure in eight years. Meanwhile, Stan Wawrinka, overcame Italy's Andreas Seppi in three sets 7-6, 7-6, 7-6. The formidable Swiss, now into his fourth Australian Open quarter-final, will play France's Jo-Wilfried Tsonga, who came from a set down to beat British surprise package Dan Evans. In the women's quarter-finals, Vandeweghe, who halted Eugenie Bouchard in the previous round, faces French Open champion Garbine Muguruza, who swamped Romania's Sorana Cirstea 6-2, 6-3. Earlier, Venus Williams also became one of the first into the last eight when she beat German qualifier Mona Barthel 6-3, 7-5. The seven-time Grand Slam winner allowed herself to dream of a possible final with her sister Serena, who is steaming through the other side of the draw in search of her 23rd major title. Her quarter-final opponent is Anastasia Pavlyuchenkova, who beat fellow Russian Svetlana Kuznetsova 6-3, 6-3 to reach her first Australian Open quarter-final in nine attempts.