The unseeded 20-year-old – on his first trip outside the US – prevailed 6-7(5/7), 6-2, 6-7(4/7), 7-6(7/4), 6-2 in sapping heat on John Cain Arena.

Shelton is into the last eight in only his second appearance at a Grand Slam and will play either another unseeded American, Tommy Paul, or Spanish 24th seed Roberto Bautista Agut for a place in the semifinals.

By reaching the last eight he joined just three other men to make the grade in Melbourne on their debut over the past two decades – Ukraine’s Alexandr Dolgopolov (2011), American Tennys Sandgren (2018) and Russian Aslan Karatsev (2021).

“It was definitely a gruelling match. There were a lot of swings throughout the match,” he said after the three hour 47 minute marathon.

“I really focused in the fifth set, just being energetic, trusting my fitness and just hustling, being courageous and I thought I did a really good job of competing at the highest level in the fifth set.

“Definitely always tough playing a friend. I’ve known JJ for a while. He’s a great guy.”

In his only previous Grand Slam appearance, as a wildcard at the US Open last year, Shelton crashed out in the first round.

A year ago the left-hander was in college at the University of Florida and ranked 569 in the world, but he has risen to 89 with his reputation growing quickly.

Nothing separated them in the opening set with Shelton’s one break point the highlight as it went to a tiebreak.

Ultimately, Wolf’s power-hitting got him over the line.

Set 2 also began as a battle of small margins, but Shelton got the first break of the match in game six when Wolf netted a volley then slapped a forehand wide, breaking again as Wolf began wilting in the afternoon heat.

Wolf removed his shoes and left the court at the changeover, returning with new attire and footwear.

In a virtual carbon copy of the opening set, it went to a tiebreak where Wolf again prevailed.

Shelton then took the fourth in another narrow tiebreak before putting his foot to the floor in the fifth.