Australian Open 2017: Roger Federer sees off Kei Nishikori in five sets
|Australian Open 2017|
|Venue: Melbourne Park, Melbourne Dates: 16-29 Jan|
|Coverage: Daily live commentary on BBC Radio 5 live sports extra; live text on selected matches on the BBC Sport website; TV highlights on BBC Two and online from 21 January.|
Roger Federer continued his remarkable return from injury by seeing off Kei Nishikori in five sets to reach his 13th Australian Open quarter-final.
The 35-year-old beat fifth seed Nishikori 6-7 (4-7) 6-4 6-1 4-6 6-3 to keep alive his hopes of an 18th Grand Slam and fifth Australian Open title.
Federer, seeded 17th, is playing his first competitive event since Wimbledon six months ago following a knee injury.
He will play Mischa Zverev, conqueror of Andy Murray, in the last eight.
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Third seed Stan Wawrinka beat Andreas Seppi 7-6 (7-2) 7-6 (7-4) 7-6 (7-4) and goes on to face Jo-Wilfried Tsonga, who beat Dan Evans 6-7 (4-7) 6-2 6-4 6-4.
After dropping his opening two service games, Federer found the range that had seen him hammer Tomas Berdych in the previous round, giving Nishikori a torrid time.
"It was a great match and a joy to be part of it," said Federer.
"I wasn't playing badly in the first set - it's a quick court and things happen fast. It was about staying calm at 4-0.
"I thought it can't get any worse from there. It was hard not to win that first set after all the effort but it paid off in the end. This is a huge win for me in my career."
- Watch highlights of day seven on BBC Two from 17:15 GMT on Sunday.
From 5-1 down, the Swiss roared back - almost taking the set before losing out in a tie-break - and clinching the second set with a solitary break.
The third disappeared in a flash as Federer took apart the Nishikori serve, winning every point on the Japanese player's second serve, and he went close to breaking through again early in the fourth set.
Nishikori, 27, held on under huge pressure and forced a decider but it was Federer who proved the stronger, racing into a 3-0 lead and closing it out - to the delight of most of those on Rod Laver Arena.
Federer played just seven events in 2016 after injuring his knee the day after his Australian Open semi-final and having arthroscopic knee surgery.
He dropped out of the world's top 10 for the first time in 734 weeks last November, and arrived in Melbourne ranked 17th - his lowest position since May 2001.
The Swiss is the oldest man to reach a Grand Slam quarter-final since the 39-year-old Jimmy Connors at the 1991 US Open.
But the departure of first Djokovic and then Murray has thrown the draw wide open, with Federer, as well as the likes of Wawrinka and Rafael Nadal, in with a chance of adding to their Grand Slam tallies.
"I felt like if Rafa and myself can be healthy, yes, you can expect us in the quarter-finals," Federer added.
"That Novak and Andy are not, that is a big surprise. I never thought that Mischa Zverev and Denis Istomin would beat those two big guys.
"I guess it's good for tennis 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."