Nadal barely put a foot wrong on Rod Laver Arena on Tuesday night, holding serve throughout a clinical 6-3 6-4 6-2 victory in one hour and 47 minutes.

Chasing his 18th grand slam title, the Spanish second seed will meet Roger Federer's fourth-round conqueror Stefanos Tsitsipas in Thursday's semi-final.

Long-time rival Novak Djokovic, who faces Kei Nishikori in Wednesday's quarter-finals, could await in the championship decider.

Nadal said it was more than he could have hoped for in his first competitive tournament since a knee injury forced him out of last year's US Open.

"The possibilities (of that happening) aren't very high," he said.

"I feel lucky to be where I am after all the things I went through, to be able to keep competing at this level.

"For me it's very emotional to be back in the semi-finals here in Melbourne.

"I had some troubles in this event during all my career. After a while without play, to be back to that semi-final means everything to me."

Yet to drop a set during a sizzling run which also included victories over Australian prodigy Alex de Minaur and Czech threat Tomas Berdych, the 32-year-old was again a model of efficiency.

Nadal lost just nine points off his first serve and only allowed Tiafoe two break point opportunities, both of which the veteran saved.

The 21-year-old Tiafoe acquitted himself well but was broken by Nadal early in each set and was unable to find the answers.

"It was tough, definitely. He's a hell of a player, man," Tiafoe said.

"His (shots) were kicking up like crazy. The court was really slow so it was hard ... he's just tough and he's played on that court so many times."

First introduced to the sport at a wealthy tennis centre in Maryland where his father was a maintenance worker, the son of immigrants from war-torn Sierra Leone will depart with plenty of admirers after an entertaining breakout run.

Nadal said it was clear the next generation were ready to knock down the door.

"I said a couple of rounds ago that they can wait for a little bit," he said.

"Looks look they don't want to wait. They are there.

"Frances here in quarter-finals, Stefanos now in the semi-finals. Going to be a great year in terms of sharing generations."

Australian Associated Press