NEW YORK – Australian Alexei Popyrin might have been the underdog on Friday but he never doubted his chances against 24-times major winner Novak Djokovic, as he executed an extraordinary 6-4 6-4 2-6 6-4 upset to reach the fourth round at the U.S. Open.

The former number one had already beaten Popyrin this year in the second round of the Australian Open and third round at Wimbledon, and fans inside Arthur Ashe Stadium expected another drubbing weeks after Djokovic won Olympic gold.

But Popyrin, who had never before gotten past the third round at a major, found another level to hand Djokovic his earliest exit from Flushing in 18 years, putting on an aggressive performance with 50 winners.

“Today was something that I kind of thought I could do,” he said. “My two experiences against him earlier this year in Australian Open and Wimbledon kind of gave me the confidence to go out there tonight and believe that I could win and actually do it and believe it.

“So when I did it, it kind of felt that kind of proved me right.”

The 28th seed arrived in New York in superb form, after beating Andrey Rublev to claim his first Masters 1000 title in Montreal earlier this month, and reached the semi-finals in Doha.

“I’ve had the capability of winning a big match but not being able to back it up,” he told reporters.

“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.”

He next plays his good friend Frances Tiafoe, who electrified crowds earlier in the day when he beat U.S. compatriot Ben Shelton in a five-set thriller.

“He’s a very tricky player. Probably has one of the best hands on tour, comes into the net a lot, likes to mix it up,” Popyrin said. “That’s going to be the tough part.” REUTERS