Veteran Andy Murray roared back in a five-set epic which ended past 4:00 am to reach the Australian Open third round with a remarkable victory over home hope Thanasi Kokkinakis early on Friday.

In front of a raucous but weary Margaret Court Arena in Melbourne, the Briton finally prevailed 4-6, 6-7 (4/7), 7-6 (7/5), 6-3, 7-5.

At five hours and 45 minutes it was the longest match in Murray's storied career.

The 35-year-old former world number one will play 24th seed Roberto Bautista Agut of Spain in round three.

The 159th-ranked Australian Kokkinakis raced into a two-set lead, giving little hint of the drama that was to come.

Kokkinakis is friends with Nick Kyrgios and displayed shades of his talented but temperamental fellow Australian, smashing his racquet as Murray mounted a trademark comeback.

Murray refused to go quietly, breaking his 26-year-old opponent to prolong the entertainment deeper into the early hours of Friday when Kokkinakis was serving for the match.

The indefatigable three-time Grand Slam champion Murray, who has a metal hip after career-saving surgery in 2019, then held his own serve for 5-5 in the third set.

Murray, now ranked 66 in the world, just would not go away and claimed the third set on a tie-break when his younger opponent put a volley wildly wide.

It was coming up to 2:00 am when Murray, who stunned Italian 13th seed Matteo Berrettini in his opening match in another five-setter, served to begin the fourth set.

By that time, some seats were empty, as weary spectators called it a night.

Still the pair battled on, with little to choose between the two combatants and every rally keenly contested.

"Why are we playing at 3 am?" shouted Murray.

They went with serve in the fourth set until Murray broke to go 4-2 up, puffing out his cheeks by way of celebration.

He then saved break point at 5-3 up and sealed the set by sending down an ace.

Murray, who rolled back the years against Berrettini, now appeared to be in the ascendancy despite being the older man and having a long injury track record.

Murray was furious after being denied a toilet break by the chair umpire at the end of the fourth set.

Kokkinakis, who had appeared to be flagging, found a second wind from somewhere at the start of the deciding set.

The crowd were on their feet at 2-2 and the noise went up a notch when Kokkinakis saved four break points at 3-3.

But as the time turned 4:00 am in Melbourne, Murray broke serve for 6-5, then held his own for a scarcely believable victory. (AFP)