In the same swift manner as one of his deadly forehands, Rafael Nadal swats away suggestions he’s unstoppable at the Australian Open.

The world No.1 has dropped just 18 games – an average of six a match – and needed less than five hours to storm into the fourth round at Melbourne Park.

He was particularly ruthless in dispatching Gael Monfils 6-1 6-2 6-3 in his latest mismatch, less than a fortnight after conceding a set against the dangerous Frenchman.

But even after capturing 11 tournaments, including the French and US Open crowns, in the past 11 months, Nadal is refusing to take any match for granted.

After knee problems curtailed his 2010 and 2011 campaigns and a virus saw him withdraw last year, Nadal knows his next setback could be just around the corner.

“No one is unstoppable,” the Spaniard said ahead of his last-16 clash with Kei Nishikori on Monday.

But he did concede his tennis against Monfils was close to perfect.

“I played a great match. Very happy the way that I played against a very tough opponent like Gael,” Nadal said.

“I have to say that I played well from everywhere. I think I played very well with my forehand – very good control of the ball.

“I didn’t lose serve during the whole match. That’s another good thing.

“That makes me feel confident, but I am in fourth round. That’s all.”

Nadal is unbeaten in five meetings with Nishikori, but is wary of Japan’s 16th seed who won the Kooyong Classic warm-up event.

“Kei is a great player. He’s able to play very aggressive, make very easy the very difficult things,” Nadal said.

“He’s very quick on the movements. Will be a very tough opponent for me.

“I think Kei is a really complete player that can play on every surface, but I think hard is the surface for him.”