Australian youngster Alexei Popyrin has caused an Adelaide International boilover, shocking Canadian world No.6 Felix Auger-Aliassime in their first-round battle.

The 23-year-old has two wins against top 10 players to his name but both were mid-match retirements.

This time the world No.120, who came through qualifying, proved he was the real deal with a 6-4 7-6 (7-5) victory to send the second seed packing.

Danish world No.11 Holger Rune was also a surprise first-round casualty, falling to Japan’s Yoshihito Nishioka.

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Sydneysider Popyrin trailed 3-0 in the second set and was also down a mini-break in the tiebreak but both times clawed his way back.

He only needed one match point to wrap up the biggest win of his career.

After a rough 2022, Popyrin said it was good to see his hard work paying off under new coach, former Belgian star Xavier Malisse, who was a top-20 player.

“I’m pretty happy. It’s obviously an unbelievable feeling,” Popyrin said on court after the match.

“I had a really, really tough season last year and to come out after qualifying and to beat a player of his quality just showed the work I did in the off season is paying off already.”

Popyrin’s match stats were impressive with 12 aces to his 22-year-old rival’s seven while he also hit 10 more winners.

Known for his booming serve, he showed he was adding to his game winning 22 points from the net – double that of Auger-Aliassime.

He said that Malisse was working to improve his consistency.

“We started in October and he’s been a great addition to my team,” he said.

“He’s trying to bring a little bit of consistency to my game.

“I’ve got the big serve, got the big forehand but I want to be more consistent.”

Popyrin next faces American Marcos Giron, who won his opening match against French veteran Richard Gasquet.

In other results, Christopher O’Connell fell to Serbian Miomir Kecmanovic 6-4 6-4 while fellow Australian Jordan Thompson also made an early departure from Memorial Drive, going down against Frenchman Quentin Halys 6-3 6-4.

Meanwhile, showcourt 1 was overflowing with fans who packed in to see former world No.1 Novak Djokovic play his first match in Australia in two years.

Playing doubles, Djokovic paired with Vasek Pospisil to take on Gonzalo Escobar and Tomislav Brkic in the first round.

Djokovic, who was deported last year ahead of the Australian Open, was warmly welcomed on to court with a loud cheer as fans queued to see the Serbian superstar in action.

But he was unable to deliver a win, falling to the doubles specialists 4-6 6-3 (10-5).