Australian Alexei Popyrin has been demolished in straight-sets by breakout American Ben Shelton in the third round of the Australian Open.

After a rousing upset of eighth seed Taylor Fritz on Thursday, Popyrin was no match for the 20-year-old Shelton and went down 6-3 7-6 (7-4) 6-4 on John Cain Arena.

Popyrin continues to search for an elusive spot in the second week of a major, having bowed out in the third round of a grand slam for the fifth time.

The left-handed Shelton's serve and forehand was on song, powering him into the fourth round in just his second grand slam.

Shelton has recently stepped up his efforts on the professional tour after playing college tennis in Florida.

His father, Bryan, played professionally for almost a decade and made the fourth round of Wimbledon in 1994.

The youngster's trip to Melbourne Park is the first time he has ventured outside of the United States.

'I would have been happy with anything in the top-100 (this time last year),' Shelton said.

'I wanted to take the process slow and not try to chase points.

'I'm really pleased with everything I've got right now, a real pinch-me moment to get through to the fourth round of the Aussie Open.

'The first 10-12 years of my life I swore I would never play tennis, it was my dad's thing.'

Shelton will face fellow American and world No.67 J.J. Wolf for a spot in the quarter-finals.

Wolf is another player to have made a stunning surge during the first grand slam of the year, having never played at a major outside of the US Open.

The 24-year-old has twice reached the third round at Flushing Meadows.