Tennis great John McEnroe believes Alex de Minaur is playing on a 'different level' - and sees no reason why he can't win a maiden Grand Slam at Melbourne Park as he has 'plenty in the tank.'

The tenth seed breezed past Italy's Flavio Cobolli on Friday night in straight sets, with Andrey Rublev his next assignment in the fourth round.

While de Minaur felt he started slowly against Cobolli, McEnroe was impressed by the local hope, who hasn't dropped a set in his three matches to date at the Australian Open.

'Obviously he was the heavy favourite, so there was some pressure to win this, show what he was made of, back-up the top 10 ranking,' he said in commentary for Channel Nine on Friday night.

'But as the match progressed, you started to see the separation between a qualifier [Cobolli] and a guy who believes maybe he can win this.

'By the end of it, Cobolli had totally tapped out. He was just - 'This guy's is too good'.

'And in the end, he was. Just a different level.

'Alex has got to be extremely satisfied with the way it ended and what little energy he needed to burn.

'He's got a lot left in the tank for the fourth round and he hopes beyond.'

If de Minaur beats fifth seed Rublev on Sunday night on Rod Laver Arena, it will be the first time the Aussie has reached the quarter-finals in his home Grand Slam.

He is now the sole Australian still alive in the singles, after Storm Hunter's dream run ended on Friday night.

The 29-year-old - who has become an instant crowd favourite - was beaten in three sets by ninth seed Barbora Krejčíková.