They admit It's like big brother versus little brother as Jordan Thompson takes on Alex de Minaur in a high-stakes all-Australian fourth-round US Open showdown in New York.
Having grown up together in Sydney, de Minaur says he's forever indebted to Thompson for taking him under his wing when the pair first met at Olympic Park more than a decade ago.
De Minaur was a wide-eyed 14-year-old, Thompson five years his senior, the cool kid with wheels and just starting to make his way in the professional ranks.
"He was the guy I was looking up to and he's always given me a lot of time," de Minaur said.
"He's helped me out a lot. I've learned a lot through him, even when he was playing the pros, the slams and I was still in the juniors.
"At Roland Garros, he would come over to (Court Suzanne) Lenglen because that's the only side the juniors are allowed and he would spend time with me."
More importantly, Thompson had something de Minaur didn't back in those days.
"I remember one of the biggest things is that he had a car," de Minaur said.
"So he would drive us to the gym, which otherwise was like a 15, 20-minute walk.
"I won't name the car but it did the job.
"So we've gone from that. Now we're putting ourselves in the deep end of tournaments and, look, it's a good problem to have that we're playing each other in the fourth round.
"It's exciting. We've grown up together."
Thompson reckons it's "unreal" for Australian tennis to be playing de Minaur for a grand slam quarter-final berth but is ready to cast friendship aside for a few hours on Monday (7am Tuesday AEST).
"Tennis is tennis," he said. "We'll be mates off the court and on the court. We'll just be going about our business.
"I mean, it is tough to play a mate but it's not the end of the world."
Despite taking out world No.7 Hubert Hurkacz and Italian seed Matteo Arnaldi, both in straight sets, en route to the last 16, Thompson is the underdog.
He's expecting to play "a lot of tough points" against his Davis Cup teammate.
"A lot of balls coming back. A great mental effort," Thompson said.
"That's why he's got to six in the world. He's been playing unbelievable tennis and he's one of the toughest competitors out there.
"So he makes it super, super tough."
De Minaur conceded he stepped up a gear or two in his scintillating third-round win over Dan Evans, having entered the tournament under a fitness cloud after being sidelined since Wimbledon with a hip injury.
"I'm trending upwards and that is exactly the way I want to be trending," he said.
The world No.10 is not content with becoming the first Australian since Lleyton Hewitt 20 years ago to reach the second week of all four slams in a single season.
"Human beings, we are never satisfied, right? We always want more,” said the French Open and Wimbledon quarter-finalist.
"A couple of years ago this was my goal, to make the second week of slams because it’s something that was so difficult for me to achieve in previous years.
"But now it's about getting (to the) deep end of tournaments. So I want to be going deep, playing with the best players in the world.
"It was a big stepping stone getting through the first week, but now the second week is when the big tournament begins, and that’s when you have got to play your best tennis.
"So hopefully I can do that."
The winner will have a huge opportunity on Wednesday (Thursday AEST) against either British world No.25 Jack Draper or unseeded Czech Tomas Machac to reach their maiden grand slam semi-final.
AUSSIES IN ACTION ON DAY EIGHT OF THE US OPEN
Men's singles, fourth round
10-Alex de Minaur v Jordan Thompson, not before 7am Tuesday (AEST)
