Roger Federer's march towards a first grand slam title in five years has continued at the Australian Open with a come-from-behind five-set win over Kei Nishikori.
The world number 17 warmed into the contest and overcame the hard-running Japanese with a 6-7 (7/4), 6-4, 6-1, 4-6, 6-3 win on Sunday night in three hours and 24 minutes.
In the night's other match, USA's Coco Vanderweghe was just too good for defending champion Angelique Kerber, winning in straight sets in 68 minutes.
Nishikori was hampered by a hip problem during the fifth set and required court-side treatment.
Federer showed his displeasure at the delay, throwing a drink bottle during the break, but remained calm on the court.
The scoreline flattered Nishikori, who lost the winners count 83-42.
"He played his heart out ... he was hanging tough and playing really well on the big points," Federer said.
"This is a huge win for me in my career."
Federer's reward is a quarter-final against German Mischa Zverev, who beat top seed Andy Murray to earn a place in the last eight.
The absence of the top two seeds has increased hopes the Swiss champion will add to his collection of 17 major titles this month in Melbourne.
Against Tom Berdych in the third round Federer was irrepressible from the get-go, but on Sunday night he took a little longer to hit full stride.
Federer didn't face a break point all night against the Czech world number 10 but on Sunday he gave away eight in his opening two service games, falling 4-0 behind.
The veteran recovered to win four games in a row in front of an energised crowd, ensuring a tiebreak.
Federer was cruelled in the tiebreak when two lets were called on points he would have won, allowing Nishikori to charge on.
A set down, the 35-year-old's imperious serving game returned.
Combined with an aggressive approach to returning Nishikori — he hit nine clean winners off the world number five's serve — Federer turned the tables.
The solitary break of the second set put Federer back on terms. He was in control after claiming the third set in 26 minutes.
Nishikori was playing under duress, showing as much when he uncharacteristically threw his racquet.
From his despair he found a way back into the match, making just three unforced errors in the fourth set to level the match.
Federer finished the stronger, perhaps due to Nishikori's troubled hip, and never looked like losing the fifth set.
The win was Federer's 200th against top-10 opposition, a record.
It also ended a four-year drought in five-set matches against a top 10 opponent.