Mount and the £48m summer signing Santos both operated in deeper midfield roles in Norway, with the former Chelsea captain backing the Brazilian, 22, to fill the void left by Casemiro's exit at the end of his contract and provide cover for the injured Manuel Ugarte.
"Andrey is a really good player. He reads the game brilliantly," Mount said. "I know he's young, but he's very experienced in going out on loan and playing in the Premier League as well.
"We're both players that want to get around it, want to put tackles in and win the ball back and be aggressive. I've really enjoyed it. It's a position that I love and that I see myself in."
Santos has started Manchester United's first two pre-season matches at number six, though he made only 13 Premier League starts on loan last season and still lacks the marquee experience some fans crave.
Mount, meanwhile, made his name further forward at Chelsea, but manager Michael Carrick is reshaping him as a fluid number eight, reviving a role Erik ten Hag had once envisaged for him before injuries derailed his Old Trafford career.
Mount added: "I've known Andrey for a while. I've watched him from afar, since he's broken into the first team at Chelsea."
The pair were briefly Chelsea teammates in early 2023, though Santos was immediately loaned out to Vasco da Gama before Mount's £60m move to Old Trafford that summer.
Mount also reflected on wearing the United captain's armband for the first time, taking over from Harry Maguire for the final 15 minutes of the first half against Rosenborg.
"I'm definitely one, but you have different types of leaders," he said. "I want to always see myself as one that leads by example and never stops working on the pitch. I've been captain previously so I love the role. Especially with a lot of younger players on the pitch, being able to speak to them and make them feel comfortable in the game and even off the pitch as well. It's a role that I really like and I loved having it in the second half."
The 27-year-old, who earned his first senior England call-up aged 19 while on loan at Derby County under Frank Lampard and won the last of his 36 caps at the 2022 World Cup, said he is feeling fitter than at any point since injuries interrupted his progress.
"I feel brilliant. I feel really, really good. I finished the season well. At the end of last season, playing a few games and being involved. Building on that momentum at the end of last season. It's been a good break, but I was ready and raring to get back and get training again. Getting back into the flow of it. Building up over these last couple of weeks. I feel really good. I feel strong and ready to go. I know we've got a few more games left and a few more weeks to really work at stuff."