Novak Djokovic showed a chink of vulnerability but survived as the world number one battled past France's Gilles Simon in a five-set thriller at the Australian Open.
Djokovic has now lost only once in his last 32 grand slam matches but he was given a scare on Rod Laver Arena, before winning 6-3 6-7 (1/7) 6-4 4-6 6-3.
The Serb was well below his brilliant best, hitting a mammoth 100 unforced errors, but he is safely through and will now meet Japan's Kei Nishikori in the quarter-finals.
The last time Djokovic was taken to a fifth was at Wimbledon last year when he held off Kevin Anderson and he showed his resilience again here to make his 27th consecutive appearance in the last eight of a grand slam.
"Playing against a player like Gilles you can expect a lot of rallies," Djokovic said.
"He is always making you play an extra shot. I made a lot of unforced errors today but he was fighting, he was playing well, physically it was very demanding and I'm just happy to get through this one."
As he was finishing his on-court interview, a spectator shouted out "no more dropshots!" after the top seed had netted two drop-shots at crucial moments in the fourth set.
#Djokovic takes advice from audience member #nomoredropshots #AusOpen Watch more https://t.co/Ek545Zh2D9 https://t.co/0f7nlx5BBY
— Australian Open (@AustralianOpen) January 24, 2016
Djokovic halted his interview and asked the fan to repeat his advice before replying over the microphone: "I hate to say it, but you're absolutely right."
Two breaks were enough in the first set but the 10-time major champion was already showing signs of sluggishness as he struggled to penetrate with his serve and made 19 unforced errors from the baseline.
Simon, renowned for his speed and guile but not his attacking instincts, was wearing his opponent down and after Djokovic had spurned 11 break points, the Frenchman capitalised, storming into a 5-0 lead in the tie-break before clinching the set.
Djokovic tightened up in the third as he reduced his error count by inviting Simon to attack and the tactic worked as he broke twice to restore his advantage.
Back Simon came again, however, and as Djokovic served to stay in the fourth set at 5-4, the top seed wavered, dabbing two limp drop-shots into the net and then missing a backhand to send the contest to a decider.
So many times Djokovic has looked jaded only to raise his game at the decisive moment, and so it proved again as he raced into a 4-1 lead in the fifth after Simon had chucked away a service game in which he led 40-0.
A wayward forehand from the Frenchman gifted away the second break and a cushion, which Djokovic needed as he was instantly broken back for 5-2.
A tense game followed as Simon saved two match points to hold but Djokovic kept his nerve, serving out with ease to seal victory in four hours and 32 minutes.
Nishikori's work-out was far less strenuous as he beat France's Jo-Wilfried Tsonga 6-4 6-2 6-4 in less than half the time - two hours and two minutes.
Nishikori (above), ranked seventh in the world, has lost all of his last four meetings with Djokovic and is under no illusions about the scale of the task ahead.
"The biggest thing is he doesn't miss," Nishikori said, "He doesn't give you any free points. I have to be the one who dictates."
World number six Tomas Berdych (above) is also safely through to the last eight after he came through his own five-setter against Spain's Roberto Bautista Agut.
Berdych lost the first set on Margaret Court Arena but outlasted Agut to win 4-6 6-4 6-3 1-6 6-3.
Four-times champion Roger Federer was in no mood to extend his Sunday too far into Monday as he raced into the quarter-finals with a 6-2 6-1 6-4 victory over David Goffin.
Federer was the last match on the main showcourt in Rod Laver Arena but because of the Djokovic-Simon game, he did not begin his fourth-round match with Goffin until 10.48pm local.
The 17-times grand slam champion established the tone for the match in the first set, which he roared through in 21 minutes as he conceded just two points on his own serve and broke the Belgian twice.
The Swiss continued to dominate on his own serve, winning more than 90% of his first service points for much of the match and hitting winners at will to seal a quarter-final against Czech Berdych in 88 minutes.
