World No.1 Rafael Nadal has battled his way into his 10th Australian Open quarter-final with a hard-earned four-set win over dogged Argentine Diego Schwartzman.
Nadal dropped his first set of the tournament before regrouping to move into the last eight with a 6-3 6-7 (4-7) 6-3 6-3 victory in three hours and 51 minutes.
Spain's 16-time grand slam champion will play 2017 Wimbledon runner-up Marin Cilic for a semi-final spot on Tuesday after the big-serving Croat recorded a similarly tough 6-7 (2-7) 6-3 7-6 (7-0) 7-6 (7-3) win over 10th seed Pablo Carrena Busta.
"A great battle," Nadal said after finally seeing off Schwartzman after three hours and 51 minutes on Rod Laver Arena.
"He's a great player in all aspects and I feel that for a lot of moments he was serving well this afternoon.
"That is something he is normally so comfortable with."
After being restricted to one match in three months before the Open, Nadal said he was finally feeling confident in his knees again and ready to make for another serious second-week push for a second title.
"It's the first big match of 2018. I started later than usual ... so one match like this probably helps," said the the 2009 Open champion and three-time runner-up.
Meanwhile hometown favourite Nick Kyrgios succumbed to world No.3 Grigor Dimitrov in a four-set thriller on Rod Laver Arena to extend the Australian Open local title drought.
Dimitrov resisted a spirited fightback from Kyrgios to end Australia's singles hopes at Melbourne Park with a 7-6 (7-3) 7-6 (7-4) 4-6 7-6 (7-4) fourth-round win on Sunday night.
The Bulgarian had the opportunity to serve out the match when he broke Kyrgios' serve to go 5-4 up in a tense fourth set, but was forced to a tiebreaker where he converted his second matchpoint.
"Playing against Nick is always tricky," Dimitrov told the Seven Network.
"Two weeks ago I lost against him ... he was serving unbelievable, playing unbelievable and competing.
"He deserves a lot of credit ... he fought really hard.
"Even when I was serving for the match I just felt it was still not over. I was still not finding my spots well and again he was playing very well.
"But I'm glad to go through the match (and win it)."
The No.3 seed will face unseeded surprise packet Kyle Edmund in the quarter- finals after the Briton defeated Italian Andreas Seppi in four sets.
Dimitrov's misfiring game forced him to scrap and scramble his way into the fourth round, but he put in his most polished performance of the tournament against Kyrgios.
And he needed to in order to overcome the most mature display under pressure of the fiery Canberran's career.
While clearly irritated by a racket stringing issue - he directed a string of terse words at his box during breaks in the opening two sets - he largely kept his infamous hot temper in check.
Despite crunching 13 aces and being utterly untroubled on serve, Kyrgios dropped an opening set he largely dominated with his first double-fault of the match in the decisive tiebreaker.
He was staring down the barrel after being broken for the first time in the seventh game of the second set to fall behind 4-3.
But Kyrgios broke an increasingly frustrated Dimitrov's serve in the fifth game of the third set.
The Bulgarian had the match on his racket when he broke to go 5-4 up in the fourth, but Kyrgios broke him to love to get back on even terms and force the thrilling tiebreaker.
The incredibly tight tussle ended with Dimitrov winning a total of 157 points to Kyrgios' 156.