The whiff of sporting upset hung around Melbourne Park on Sunday after top seeds Andy Murray and Angelique Kerber were handed stunning defeats in the Australian Open fourth round.Britain’s Murray was bamboozled by the serve-volley game of Mischa Zverev to exit after 3-1/2 hours on Rod Laver Arena, while fellow world number one Kerber’s title defence was ended in little more than an hour by Coco Vandeweghe. (Also read: Australian Open: Top-seed Andy Murray knocked out in fourth round by Mischa Zverev)Murray was the first top seed to depart before the quarter-finals since Lleyton Hewitt in 2003, while Germany’s reigning women’s champion was last sent packing before the second week a decade ago when Amelie Mauresmo went out in the fourth round.Murray and Kerber were playing their first grand slams as top seeds and both looked all but powerless to deal with the style of game they were confronted with from across the net. (Also read: Australian Open: Top seed Angelique Kerber knocked out by unseeded Coco Vandeweghe in fourth round)Zverev, the world number 50, rushed the net 118 times to keep one of the best defensive players in the game on the backfoot for much of the contest before holding his nerve to close out the contest 7-5, 5-7, 6-2, 6-4.”Credit to him,” said Murray. “He came up with great, great shots and played a really, really good match. You know, you always finish matches you lose with things you maybe could have done a bit better, but he played some really good stuff.”advertisementThe German, ranked outside the top 1,000 in the world after wrist surgery two years ago, will face Roger Federer in his maiden grand slam quarter-final after the Swiss master outlasted Kei Nishikori 6-7(4), 6-4, 6-1, 4-6, 6-3. (Also read: Defending champion Novak Djokovic crashes out of Australian Open)New Yorker Vandeweghe later hammered down 30 winners to Kerber’s seven, overpowering the U.S. Open champion 6-2, 6-3 to set up a meeting with Spanish seventh seed Garbine Muguruza in her first trip to the last eight in Melbourne.Kerber made 15 unforced errors in a contest asting little more than an hour and admitted it was simply not her day. (Also read: Roger Federer avoids upset dramas at Australian Open)”It was a tough match and, of course, I’m disappointed,” she said. “But I was not feeling the ball at all tonight. I was not playing good from the first point.”I was trying tonight but, yeah I missed a lot. So this was not my game like I play normally.”TOP RANKINGWhile Kerber could yet lose the number one ranking to Serena Williams after the year’s first grand slam, Murray’s main rival Novak Djokovic made an even earlier exit in the second round.With Murray and the Serbian reigning champion having already departed, Melbourne Park will next week witness the first grand slam since the 2004 French Open without its top two men’s seeds.Federer will hope to profit as he bids for his 18th grand slam title, as will his compatriot and 2014 champion Stan Wawrinka, who is in the same half of the draw and fended off Andreas Seppi 7-6(2), 7-6(4), 7-6(4).Wawrinka next faces France’s 2008 finalist Jo-Wilfried Tsonga, who ended the fairytale run of Britain’s Dan Evans by coming from a set down to win 6-7(4), 6-2, 6-4, 6-4 on Hisense Arena.Murray and Evans had hoped to become the first British pair to reach the men’s quarter-finals at Melbourne Park in 40 years and the first at a grand slam since Tim Henman and Greg Rusedski at Wimbledon in 1997.Venus Williams, at 36 the oldest woman in the singles draw, also progressed to the last eight with a 6-3, 7-5 victory over Mona Barthel, moving closer to a potential blockbuster final against sister Serena.The younger Williams sister continues her quest for a 23rd grand slam title against Barbora Strycova on Monday, when men’s 2009 champion Rafa Nadal is also in fourth round action.