Britain's Andy Murray reacts after losing his Men's singles fourth round match against Germany's Mischa Zverev in Melbourne, Australia on Jan 22, 2017. [Photo/IC]

MELBOURNE — Andy Murray and Angelique Kerber had much in common heading into the first Grand Slam of the season as the No 1 seeds.

They shared an unwanted link on Sunday, though, when both were upset in the fourth round of the Australian Open.

By the end of a chaotic first week at Melbourne Park, five-time finalist Murray had extended his Australian drought following a 7-5, 5-7, 6-2, 6-4 loss to No. 50-ranked Mischa Zverev a matter of hours before defending women's champion Kerber lost 6-3, 6-2 to CoCo Vandeweghe in an upset that finished at six minutes past midnight.

Novak Djokovic, who beat Murray in finals to win four of his record six Australian titles, didn't make it past the second round. Multiple major winners Roger Federer and Rafael Nadal, both returning from injury layoffs, needed come-from-behind wins to advance to the second week.

Another six-time champion, Serena Williams, is still on track for a record 23rd major title and will get the second week started on center court.

It was tough at the top on Sunday for Murray and Kerber.

"Right now I'm obviously very down because I wanted to go further in this event," Murray said. "I've had tough losses in my career in the past. I've come back from them. This is a tough one."Kerber said: "Of course, they are new experiences ... new challenges," Kerber said. "I can learn from all the other stuff which is new for me."Against Vandeweghe, she said she was "trying everything, but I missed a lot and I make a lot of unforced errors — this was not my game."Vandeweghe had never been past the third round at the Australian Open, and lost in the first round here last year. But she pounded Kerber with a powerful forehand, clubbing 13 of her 30 winners from that side.

After match point, she shrugged her shoulders in a "so-what" motion after moving into a quarterfinal against French Open winner Garbine Muguruza.

"It's the first time I've ever beaten a world No. 1," the 35th-ranked American said. "And especially at a Grand Slam, I think it makes it that much sweeter."Kerber saved a match point in the first round last year before winning her first major title, beating Serena Williams in the final. She replaced Williams atop the rankings after winning the US Open. Now Williams can regain the top spot — if she wins the title here.

Murray rebounded last year from his Australian and French Open finals defeats to replace Djokovic at No. 1.