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 yesterday. 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.

"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."