Roundup: Three top seeds out of Australian Open before quarterfinals

The dream of a Roger Federer vs Rafael Nadal Australian Open final is alive and well after the Swiss ace dispatched Japan's Kei Nishikori in a grueling five set battle while defending champion Angelique Kerber went home in straight sets on Sunday night.

It took the veteran three hours 24 minutes to defeat the world No. 5 Nishikori 6-7(4), 6-4, 6-1, 4-6, 6-3 to celebrate his 200th career win against a top 10 player, wrestling the match back in his after after a quick start from the Japanese star.

"That put me on the back foot for the remainder of the match to some extent," Federer told reporters after the match.

The Swiss ace didn't think he would get back into that first set, but momentum shifted his way before Nishikori read the right shots at the right time in the tiebreaker.

"It was a tough set to lose," Federer said.

"But, I was still upbeat about my chance after that first set, I think it gave me something coming back into that set actually."

The win has set up up for a strong finish with a favourable Australian crowd lifting Federer in the important moments, especially in the fourth and fifth set which were driving him to the win, and hopefully another Australian Open finals berth.

Federer will meet Germany's Mischa Zverev in the quarter final on Tuesday after the Moscow born world No. 50 defeated world No. 1 Andy Murray 7-5, 5-7, 6-2, 6-4 in a little over three and a half hours, playing "the best match of my life" in the match prior.

It's the first time in 15-years the Australian Open' s top seeds haven' t made it to the quarter finals after world No. 2 Novak Djokovic lost former world No. 33 -- currently ranked 117 -- Denis Istomin -- who won the Asian wild card playoff to qualify for the Australian Open -- on Thursday night. Istomin won 7-6 (8), 5-7, 2-6, 7-6 (5), 6-4 in a near five hour marathon.

The Uzbekistani however will face Bulgarian Grigor Dimitrov in their round four clash as he continues his dream run, but it will be a tough task with the world No. 15 defeating Istomin at their last encounter. Dimitrov won in straight sets (6-3, 6-3) at the 2014 Shanghai ATP World Tour Masters.

Meanwhile Rafael Nadal will face his toughest test of his campaign, Frenchman Gael Monfils as Australia quietly hopes he and Federer will meet in the final on Sunday night. Federer and Nadal are on opposite sides of the draw, though semifinal clashes are always tough.

The prospect of Nadal and Federer being the quarter finals could be expected if they were both fit and healthy, however Djokovic and Murray being absent is "a big surprise."

"I never thought that Mischa Zverev and Denis Istomin would beat those two big guys," Federer said.

"I guess it's good for tennis, you know, that a lot of guys believe stronger now that the top guys are beatable, are vulnerable, especially on a faster court. It happened completely in different circumstances.

"But two huge surprises, no doubt about that."

The prospect of a Williams Sisters final is also growing after Venus Williams continued her march after a straight sets win over German qualifier Mona Barthel.

"That could hopefully happen, (but) we both still have to work very hard to get there," Williams told reporters after her 6-3, 7-5 win.

Williams has yet to drop a set in her Australian Open campaign, but "it doesn't matter who you come up against" as everyone, including qualifiers, are playing to win.

"They have nothing to lose," Williams said.

"I'm going to be focused on winning one round at a time and focus on doing what it takes to be there."

Williams faces Russian Anastasia Pavlyuchenkova in the quarterfinals, before a potential semifinal berth against either world no. 7 Garbine Muguruza or fellow compatriot Coco Vandeweghe.

Vandeweghe defeated defending Australian Open champion and currently world No. 1 Angelique Kerber in a convincing 6-2, 6-3 fashion, ending the German's hopes of repeating her breakthrough open performance.

"It was a tough match and of course I'm disappointed (with losing) " the Australian Open top seed told reporters.

"I was not feeling the ball at all tonight, I was not playing good from the first point, so yeah, it was not my match, for sure."

The newly minted world no. 1 conceded it was "a little bit difficult" to get used the new expectations placed on her, but "when the tournament (started), I was doing all the things like I did last year, (I) was trying to do everything simple."

"My preparation was like I wanted and everything was fine," Kerber said.

"I came here to play good tennis, playing round by round, trying to continue my run from last year.

"But this is tennis, and you have good days and bad days. For sure today was not my best day."

Serena Williams will face world no. 16 Barbora Strycova first up on Monday. Endit