Nick Kyrgios believes Alexei Popyrin is on the cusp of something special, tipping his fellow Australian for big things after his US Open run.

Ranked outside the top 50 a month ago and never before having ventured beyond the third round of a grand slam, Popyrin is being branded the new "Wizard of Oz" after slaying Novak Djokovic in one of tennis's colossal upsets.

And Kyrgios was paying attention, tipping Popyrin as being a future grand slam winner.

"I got a feeling Pop is about to turn into a superstar," Kyrgios wrote on X.

"Next year will be his best year.

"His consistency is something I was looking for my whole career. Genuinely happy, man. 

Despite that approval marrying what Djokovic himself said of his vanquisher, Popyrin is ignoring the hype, sticking stubbornly to his "stay in the now" mantra as Australia's emerging star continues his audacious quest for US Open glory.

With Djokovic joining reigning French Open and Wimbledon champion Carlos Alcaraz on the Open scrap heap, Popyrin has earned himself a serious opportunity to go deep in New York.

The 25-year-old faces world number 20 Frances Tiafoe on Sunday (9am Monday AEST) for a place in the last eight.

The victor will play either sixth seed Andrey Rublev, who Popyrin beat in last month's Montreal Masters final, or ninth seed Grigor Dimitrov in the quarter-finals, with world number four Alexander Zverev the highest-ranked player left in the bottom half of the draw.

Popyrin is aware of the growing excitement but refusing to stray from the immediate task at hand.

"I'm not thinking that far. I'm going to give you the cliché answer I always give: It's always the next match for me. I focus on the next match and that's it," he said.

"My focus is on Frances. If I get past that, then we'll focus on the next one.

"The biggest part about Montreal was I was able to back up big wins. For me, that's something that I have really had to work on.

"I've had the capability of winning a big match but not being able to back it up. This week and Montreal I was able to do that.

"Hopefully I can continue it this week because this is probably the biggest win of my career so far, ranking-wise [beating Djokovic]."

Tiafoe looms as a formidable challenge.

A semi-finalist two years ago, when he lost to eventual champion Alcaraz, and quarter-finalist in 2023, the American loves the big stage, playing in front of home fans at Arthur Ashe Stadium.

Tiafoe's showdown with Popyrin has not surprisingly been afforded the prime time slot on Sunday night in New York.

"He's actually a really good friend of mine," Popyrin said of his last-16 rival.

"We get along really well off the court. It will be interesting to play against him. We have practised a bunch of times.

"Yeah, he's a very tricky player. Probably has some of the best hands on tour, comes into the net a lot, likes to mix it up.

"That's going to be the tough part. I'm just going to have to play my game, serve well.

"I felt like I didn't really serve that well [against Djokovic], considering the percentages and stuff.

"I've got to have to improve on that."

AAP/ABC