Murray turns back the clock to fell Berrettini in five-set epic

With the crowd largely in the palm of his hand, the Scot raced out of the blocks to take the first two sets under the roof of a muggy Rod Laver Arena.

A five-time runner-up in the tournament, little has come easy for Murray at Melbourne Park, and so it proved again as Berrettini emerged from a long off-court break between sets dialled-in to level the match.

Murray's determination never wavered, though, and he held his nerve in the deciding 10-point tiebreak, closing out the match with incredible fortune as his bunted forehand return caught the net and left Berrettini no chance.

"I'll be feeling this this evening and tomorrow but right now I'm just unbelievably happy, just proud of myself," Murray said on court after the four-hour 49-minute slog.

"I put a lot of work into the last few months with my team who are here to give me the opportunity to perform in stadiums like this ... and it paid off tonight."

Murray will play the winner of Australia's Thanasi Kokkinakis and Italian veteran Fabio Fognini for a place in the third round.

The 35-year-old might have saved his legs a couple of hours' work had he converted a break point when up 2-1 in the third set but the golden chance went begging when he meekly netted a forehand.

Berrettini made the most of his reprieve and served like a machine to put the match on level terms, even as a hard-running Murray channelled his halcyon days of 2016 and produced a highlight reel of angled winners.

For a moment it appeared Berrettini was set to prove Murray's Grand Slam nemesis once again, having knocked him out of the third round of the U.S. Open four months ago.

The Italian, a semi-finalist last year, unleashed a thumping return at 5-4 up in the fifth set to bring up match point.

More out of hope than design, Murray lobbed over an ill-judged drop-shot that Berrettini swooped on, only to hit his passing shot straight into the net and leave fans gasping.

The match then slid through the Italian's fingers as Murray raced to a 6-1 lead in the tiebreak before savouring a helpful kiss from the net to advance.

Having won seven out of eight of his previous five-set matches, it was a cruel way for Berrettini to go out, especially after clawing back to 8-6 in the tiebreak.

But the 26-year-old could only doff his cap to the seasoned Scot, who gave his metal hip a proper workout.

"Could have been, you know, different just with a different ball," he said.

"It's impressive what he could do after so many surgeries, after all the kilometers that he ran in his career.

"It just shows how much he loves the game, how much he loves these kind of matches."