After six months out of the game, Roger Federer's fairytale return continued under the lights of Rod Laver Arena where he emphatically quashed doubts about his fitness in three hours and 24 minutes of high-octane tennis to see off fifth seed Kei Nishikori 6-7(4) 6-4 6-1 4-6 6-3 on Sunday to reach the Australian Open quarter-finals.
Having stormed into the match after a 90-minute demolition of Tomas Berdych, 35-year-old Federer showed his appetite for a grind, going toe-to-toe with the fleet-footed Japanese in a match littered with marathon points.
"He played a great match... it was a joy to be a part of," the Swiss 17th seed said after sealing the contest with a huge smash down the line. "This is an important win for me in my career. I know he's got a great five-set record and he's a tough customer."
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Federer will play Mischa Zverev for a place in the semi-finals, the German having earlier upset top seed Andy Murray on the same centre court.
With second seed Novak Djokovic also eliminated, Federer holds genuine hope of ending his five-year wait to add to his record 17 grand slam titles.
Those hopes seemed in vain for a period against Nishikori as Asia's first men's grand slam finalist roared to a 4-0 lead before weathering a Federer fightback to take the first set on a tiebreak.
The Swiss recovered quickly, however, belting a huge return to break Nishikori in the seventh game of the second.
Federer served out the set to love when Nishikori hit a return into the tramlines and the old master threw a steely gaze at his player's box, pumping his fist.
Rattled by the pressure, Nishikori became twitchy, his fidgeting between points betraying the nerves as Federer roared through the third set in 26 minutes.
The Swiss looked to be coasting to victory but he suffered a rare wobble at 2-2 in the fourth, shanking a straightforward smash and then netting a volley to give up two break points.
The door ajar, Nishikori barged through it with a stinging passing shot as Federer rushed the net with more hope than design.
Nishikori served out to love, the match back to level terms as Federer's suddenly misbehaving backhand put a return just wide of the line.
Nishikori took a medical time-out between sets, with a trainer working hard on his legs, but it was Federer who appeared in greater need of a massage as he was thrown around the court by the Japanese.
But he held on grimly, and grabbed his chance in the second game when Nishikori netted to offer two break points.
Nishikori saved the first and fired a huge serve on the next that should have settled the argument.
But Federer somehow made the return with a desperate backhand lunge and Nishikori ignored the offer of an open court to dump the ball into the net, triggering thunderous cheers from the terraces.
Federer rode the momentum to the finish, serving out the match strongly and savouring a huge ovation from the Rod Laver Arena crowd after defying father time once again.