Shelton gets better of Popyrin and 'rowdy' crowd to roar into last 16

Shelton had never travelled on Tour outside the United States until this year and barely turned heads in the warm-up tournaments in Adelaide and Auckland before bursting onto the scene in Melbourne.

The 20-year-old was virtually unstoppable on serve as he slammed the door shut on every opportunity Popyrin had to break while the American also fired 34 winners in front of a partisan crowd that had hoped to see another Australian advance.

"I know I came from college tennis and I really thought it was rowdy there, but this stadium is something special," a grinning Shelton said.

"I know that you guys were going for your hometown boy today and I didn't have most of the crowd on my side," he added, even as the fans roared their approval.

Novak Djokovic and Andy Murray were in action at the same time on Rod Laver Arena and Margaret Court Arena but the John Cain Arena still had a healthy turnout after a helping hand from Alex de Minaur, who had urged the locals to get behind 'Popeye'.

"Us Aussies, we stick together," De Minaur had said in a post-match interview after the home fans watched him beat Benjamin Bonzi at Rod Laver Arena.

A colourful crowd got in on the act, even attempting a Mexican wave at one point, but they were quickly subdued when Shelton broke midway through the opening set as the American's celebratory scream echoed around the arena.

The fans found their voice again in the second set when Popyrin took it to a tiebreak but Shelton was undeterred, silencing them again with both his firepower and finesse, closing out the set with another roar.

They could only look on in dismay as Popyrin soon lost his range and his unforced error count climbed, gifting Shelton the advantage before finding the net on match point to give the young American the win in exactly two hours.

A year ago, Shelton was ranked 570 but has now climbed into the top 100 and could even break into the top 50 with a deep run at the tournament - a phenomenal achievement for someone who did not want to play tennis until he was a teenager.

"For the first 12 or 13 years of my life, I swore that I would never play tennis. That was my dad's thing and I was going to let him have it," he said, referring to his father Bryan who reached a career-high ranking of 55 in the 1990s.

"But yeah, I kind of fell in love with the sport and here we are. So hopefully I can make a career out of it."