A place in the last eight of the US Open — and inside the world’s top 20 — is on the line for Australian star Alexei Popyrin when he takes on American Frances Tiafoe at the US Open on Monday morning (AEST).

After stunning the tennis world on Saturday by beating reigning champion Novak Djokovic, the 28th-seeded Australian faces a tough task against local hope Tiafoe, who is seeded 20th.

The two are good friends but have never met on tour before a meeting to determine who will face ninth-seeded Grigor Dimitrov in the quarterfinals.

“We get along really well off the field,” Popyrin said of Tiafoe. “It will be interesting to play against him. We’ve practiced a few times.

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“He’s a very tough player. (He) probably has one of the best hands on tour, comes to the net a lot (and) likes to mix it up. That’s going to be the tough part. I’m just going to have to play my game (and) serve well.”

The 25-year-old’s victory over Djokovic continued his remarkable rise, which was highlighted by his maiden ATP Masters title in Montreal.

A win would not only put Popyrin in the quarterfinals of a Grand Slam tournament for the first time in history, but also put him in the world’s top 20. That’s remarkable for a player who was outside the top 100 less than two years ago.

Australia are certain to have at least one player in the last eight as Alex de Minaur and Jordan Thompson face off in the round of 16 on Tuesday (AEST).

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SECOND SET

Alexei Popyrin has squandered a golden opportunity to level his US Open round of 16 match with American favourite Frances Tiafoe and now faces a daunting task of triumph.

After losing the first set 6-4, the Australian held three set points to level the score at 5-3 in the second set, but failed to score as Tiafoe came back to secure the tiebreak.

The 20th seed now leads 6-4 7-6 (3) in the fourth round match currently underway at Arthur Ashe Stadium.

Not only is it an opportunity that no longer exists for the Australian, the partisan crowd in attendance is now cheering for Tiafoe, a Washington DC-raised star who is a fan favourite in America.

Popyrin dominated his serve for a while and eventually found his range from the baseline. Later, however, he started to regress in both areas, making it increasingly difficult to reach his first Grand Slam quarterfinal.

Popyrin said on Friday night, when he was put under pressure to beat Djokvic in four sets, he started cursing himself to cheer himself up and finish the legend.

As the level of the match rose early in the second set, exemplified by Tiafoe’s screaming backhand winner in the third game, Popyrin could be heard pushing for more.

It was a test for the Australian as his inspired rival began to snare winners.

With a break point at 1-all, Popyrin was able to fend off the first challenge with a serve aimed at his rival’s body. When he finally held, he roared defiantly towards his box.

A full set after an initial challenge with the Tiafoe serve, a new chance for Popyrin as, after a few early mistakes, he finally found his range from the baseline.

The 25-year-old was down 30-0 but still scored four great points in a row, combining winning passes with excellent play on the court, drop shots and lobs, strong defense and a quick transition to attack.

The moment to force the break was exemplary, with Popyrin’s touch coming to the fore as he executed a drop shot that sent his rival into the net, before volleying past him.

The Sydney player did everything he could, except secure the set by serving at 5-3 to take a 40-0 lead, but he gave his rival a huge reprieve.

After a few errors during the rallies, Tiafoe saved a third set point by hitting a backhand return for the winning set, before Popyrin double-faulted on break point.

Popyrin started the tiebreak poorly with a double fault – his third of the set – and then hit a forehand that was too high when he was in a good position to score the second point.

When Tiafoe hit a crosscourt forehand pass shot on the next point, the crowd jumped to their feet to celebrate, putting the local favorite in a strong position in the tiebreak.

After Popyrin double-faulted in the tiebreaker for the second time to trail 3-6, it was Tiafoe who held on to three set points. And he made no mistake as he fired an ace past the Aussie.

FIRST SET

The Australian served well for much of the set, hitting eight aces, but paid the price for his mistakes with his forehand wing, both when holding and when facing break points in the set.

The 28th-seeded player is much more aggressive than his rival, who reached the semi-finals in New York two years ago, but the riskier strategy has seen him make many more mistakes than his rival.

In a match where service is likely to rule, the Australian will need to improve his game to progress after his stunning victory over Novak Djokovic two nights ago.

Popyrin was wearing headphones when he was introduced, which may have been a wise move at first to drown out the first signs of support for the local candidate.

While the Aussie received warm applause, the ovation for Tiafoe was deafening, even with the 24,000-seat stadium still not completely full. And there was a roar when he broke his serve to take the lead deep in the opening set.

Tiafoe won the toss but decided to return anyway, clearly hoping the Australian would be nervous on his return to the court where he defeated Novak Djokovic two nights ago.

Popyrin was initially unaffected by this, as he hit his first service game in less than a minute, thanks in part to two aces at the T to the advantage court.

In an impressive service start, the 28th-seeded player played his first four points on the deuce court, aces, with the Australian adding a few more points in his second service game.

An off-backhand winning shot on the return on the opening point of Tiafoe’s second service game continued Popyrin’s promising start and gave him the first break points of the round of 16 match.

But he couldn’t capitalize on the chance. With an aggressive forehand he hit the net cord and one of the two chances he created was converted.

The course of the match was in stark contrast to his victory over Djokovic, which is not surprising given that the Serb is perhaps the greatest player tennis has ever seen.

The American relies more on his forehand and power than his return and converted just one of three break points leading up to the fourth-round match, while Popyrin’s conversion rate during the tournament was 53 percent.

It was rare for rallies to last long, which is not surprising given the strengths of both players.

A pair of double faults in a row allowed Tiafoe to take a service game from Popyrin (3-3), but the three-time ATP Tour title winner hit a forehand winner to relieve the pressure.

But when he served at 4-4, he made a pair of forehand errors — an overhit on the second point and another trying to reach the sideline on the fifth — to give the American his first chance to break. When the Australian hit another forehand long, Tiafoe took control.