Time to step up as Nadal fights into quarters

Rafael Nadal says it's time to step up at the Australian Open after fighting off tenacious Argentine Diego Schwartzman to win through to the quarter-finals on Sunday.

The 2009 winner was taken to four physically-demanding sets in almost four hours before prevailing 6-3, 6-7 (4/7), 6-3, 6-3 on Rod Laver Arena, ensuring he remains world number one after the tournament ends.

It will be his 10th Australian Open quarter-final appearance, second only to Roger Federer, and he will face Croatia's sixth seed Marin Cilic. Nadal leads 5-1 in their previous meetings.

"Now we start the second week in the quarter-finals. Now is the moment to make a step forward, to play more aggressive," the Spanish top seed said.

"I know I'm going to have a tough opponent in Cilic. I need to play aggressive and play well. That's what I'm gonna try."

It was just the physical examination Nadal was looking for after coming into the year's opening Grand Slam without an official match following knee concerns.

"It was a good test but at the same time I prefer to win in two hours than in four," Nadal said. "But moments like this helps to be more confident in yourself, in your body."

It was the Spaniard's fourth win over the Argentine but his toughest after beating him in straight sets in the second round at the 2015 US Open.

"Diego played well and he played aggressive. He did a lot of things well, and I didn't play as aggressive as I did last couple of days," said Nadal, whose win ensured he will remain No.1 when the new rankings are released the day after the Open ends.

"Of course, I feel little bit tired, but yeah good. I was able to keep fighting until the end.

"It is the first big match I played in 2018. I started later than usual so a match like this probably helps because you know that helps confidence in myself.

"That's confidence knowing that I can resist almost four hours on court playing at a good intensity."

- Best in history -

Nadal broke in the eighth game on the way to taking the opening set, but he encountered stiff resistance in the second set.

There were six service breaks as Nadal could not shake off the tigerish Argentine, who levelled the match by winning the tiebreaker when the top seed's forehand was long.

There was an exhilarating moment when Schwartzman ran down a drop shot and won the point with an angled volley across the net to break back at 4-4.

Nadal took control in the third set with a break in the fourth game, but he had to fight off five break points before holding serve in a titanic 13-minute second game in the final set.

He broke in the third game of the fourth set, but had to make some monumental holds of service to keep Schwartzman at bay, winning on his third match point with a return winner.

Diminutive 76th-ranked Schwartzman, a quarter-finalist at last year's US Open, was bidding to reach the last eight for the first time in Melbourne.

He endeared the crowd with the scampering around the court and his astonishingly powerful groundstrokes for one so small in stature.

"I had many chances in the start of every set, having a lot of break points, and I couldn't win those points," Schwartzman said.

"Rafa played good points in those moments, playing aggressive. That's why he's one of the best in history."