Melbourne - Rafael Nadal battled through a huge test to make his 10th Australian Open quarter-final on Sunday.
On an overcast and muggy day at Melbourne Park, the Spanish world number one was up against his most dangerous opponent yet in pocket-rocket Diego Schwartzman, one of the smallest men on tour.
The Argentine 24th seed endeared with his astonishingly powerful groundstrokes before Nadal prevailed 6-3, 6-7 (4/7), 6-3, 6-3 in almost four hours on Rod Laver Arena.
It kept alive his push for a 17th Grand Slam title and also ensured he will remain number one will the new rankings come out after the tournament ends.
"It was a great battle," said Nadal, who is chasing his second Melbourne title after beating Roger Federer in the 2009 final.
"Of course, I feel little bit tired, but I was able to keep fighting until the end."
He will play sixth seed Marin Cilic for a place in the semi-finals after the Croat beat Spanish 10th seed Pablo Correna Busta 6-7 (2/7), 6-3, 7-6 (7/0), 7-6 (7/3).
The win was Cilic's 100th at a Grand Slam.
"I have played great tennis from the first round against tough opponents and now I am really looking to the next match, it will be definitely be a big challenge," he said of the Nadal clash.
Ordinarily Nadal, as the top seed, would have top billing on Rod Laver in the evening, but not with local star Nick Kyrgios in action.
The maturing Australian 22-year-old dispatched French veteran Jo-Wilfried Tsonga in the last round and faces third seed Grigor Dimitrov later.
The winner will play Briton Kyle Edmund, who reached his first Grand Slam quarter-final with a 6-7 (4/7), 7-5, 6-2, 6-3 win over Italy's Andreas Seppi.