They admit it’s like a battle between big brother and little brother when Jordan Thompson takes on Alex de Minaur in an all-Australian high-scoring duel in the fourth round of the US Open in New York on Tuesday.

De Minaur, who grew up together in Sydney, said he is eternally grateful to Thompson for taking him under his wing when the two first met at Olympic Park over a decade ago.

De Minaur was a wide-eyed 14-year-old, Thompson was five years older than him and was just starting his career as a professional.

“He was the guy I looked up to and he always devoted a lot of time to me,” de Minaur said.

“He helped me a lot. I learned a lot from him, even when he was playing professionally, at the Grand Slam tournaments, and I was still a junior.

“At Roland Garros, he would come to (Court Suzanne) Lenglen because that is the only team allowed for juniors and he would spend time with me.”

And more importantly, Thompson had something that de Minaur didn’t have at the time.

“I remember one of the most important things was that he had a car,” de Minaur said.

“So he drove us to the gym, which would otherwise have been a 15 to 20 minute walk.

“I won’t mention the name of the car, but it served its purpose.

“So we’ve said goodbye to that. Now we’re jumping into the deep end of tournaments and you see, it’s a good problem that we’re playing against each other in the fourth round.

“It’s exciting. We’ve grown up together.”

Thompson believes it is “unrealistic” that the Australian tennis player will play de Minaur for a place in the quarter-finals of a Grand Slam tournament, but is willing to give up the friendship for a few hours from around 7am (AEST) on Tuesday morning.

“Tennis is tennis,” he said.

“We’ll be friends on the pitch and off the pitch. We’ll just go about our business.”

“I mean, it’s hard playing a buddy, but it’s not the end of the world.”

Although he defeated world number seven Hubert Hurkacz and Italian seed Matteo Arnaldi in straight sets, Thompson is the underdog.

He expects to play “many difficult points” against his Davis Cup teammate.

“A lot of balls are coming back. A great mental effort,” Thompson said.

“That’s why he’s number six in the world. He plays incredible tennis and is one of the toughest competitors out there.

“So he makes it super, super difficult.”

De Minaur admitted that he had stepped up a gear in his spectacular third-round win over Dan Evans after having been sidelined since Wimbledon with a hip injury and therefore entering the tournament in poor fitness.

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“My trend is up, and that’s exactly the direction I want to go,” he said.

The world number ten is not satisfied with being the first Australian since Lleyton Hewitt 20 years ago to reach the second week of all four Grand Slam tournaments in a single season.

“We humans are never satisfied, are we? We always want more,” said the quarter-finalist of the French Open and Wimbledon.

“A few years ago, my goal was to reach the second week of the Grand Slam tournaments because it had been so difficult for me in previous years.

“But now it’s about getting far in tournaments. So I want to get far and play with the best players in the world.

“It was a big step to get through the first week, but now the big tournament starts in the second week and you have to play your best tennis.”

“So I hope I can do it.”

The winner has a great chance of reaching his first Grand Slam semi-final on Thursday (AEST) against British world number 25 Jack Draper or unseeded Czech Tomas Machac.

Australian Alexei Popyrin was scheduled to face American Frances Tiafoe in the fourth round on Monday morning from 9am (AEST).

AAP