UPDATED: Thanasi Kokkinakis scored a big upset win over Greek star Stefanos Tsitsipas to headline a terrific day for Australian men at the US Open, with Chris O’Connell also knocking out a seed and top hope Alex de Minaur progressing to the second round in four sets.

As 11th seed Tsitsipas experienced more turbulence since splitting with his father as coach, Kokkinakis took full advantage to win 7-6, 4-6, 6-3, 7-5 in a rugged four hour match at Flushing Meadows on Wednesday (AEST).

Amid plenty of support from the New York crowd who cheered the underdog against the No.11 seed, Kokkinakis hammered 17 aces to score the biggest victory of his grand slam career.

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“Incredible. You guys (the crowd) were unbelievable. He’s 11 in the world and I felt all the support,” Kokkinakis said.

“Four hours in extreme heat against one of the best players in the world.

“Hell of a player. I had a five set battle with him a couple years ago at the Australian Open. I was expecting a war. It was physical out there.

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“I have a tendency to sometimes drag these matches on. I tried to stay focused and stay the course. I tried to play every point.

“I had a lot of tight losses when I’ve been in winning positions. That was just all relief and mental I would say. I’m super excited.”

Despite making the US Open boys’ final in his junior days, Kokkinakis has experienced limited success at senior level, with the victory over Tsitsipas just his second ever in New York and his first since 2019 due to several injury plagued seasons.

After taking the first set and then going down in the second, Kokkinakis received treatment to his thigh in the third set, which seemed to give him more of an edge as the match wore on.

Kokkinakis next faces unseeded Nuno Borges.

He was not the only Australian to progress to the second round at Flushing Meadows.

World No.10 de Minaur got through with a four set win over Marcos Giron, while Jordan Thompson defeated Frenchman Constant Lestienne 6-1, 6-3, 6-2.

Tristan Schoolkate came from two sets down to beat Japan’s Taro Daniel 4-6, 4-6, 6-4, 7-6, 6-4 while Chris O’Connell pulled off a big upset by beating Nicolas Jarry, the 26th seed from Chile, 6-4, 6-3, 4-6, 6-3.

Max Purcell beat compatriot Alex Vukic 7-5, 6-4, 6-3 while James Duckworth fell 6-1, 4-6, 6-4, 6-4 to Flavio Cobolli, the 31st seed from Italy.

Little-known Li Tu then stunned Carlos Alcaraz by winning the second set and cupping his hand to his ear before losing 6-2, 4-6, 6-3, 6-1 to the Spanish superstar.

Tu, 28, was once a teenage prodigy who battled with Kokkinakis for the mantle of Australia’s No.1 junior in his age group.

Ten Aussies are now through to the second round with Alexei Popyrin, Ajla Tomljanovic, Rinky Hijikata and Maya Joint having won their singles matches on day one of the tournament.

The last time eight Australians advanced to the second round in the US Open men’s singles competition was 1976.

In the women’s draw on Wednesday (AEST), Australia’s Daria Saville, Priscilla Hon, Arina Rodionova, Destanee Aiava and Taylah Preston suffered first round defeats.

– with Sam Worthington