The two Hollywood stars were in their teens when they worked on Francis Ford Coppola's 1983 movie The Outsiders together, and they had to find ways to kill the time when they were "stuck on location".
Appearing on The Rich Eisen Show, Lowe recalled: "(Cruise is) so competitive that we used to box in the hallway of the hotel we were staying at during Outsiders.
Rob Lowe (second from left) and Tom Cruise (right) were teenagers when they filmed The Outsiders. (AP PHOTO)
"So much testosterone. We're 18-year-old guys stuck on location. So we would wear headgear, and we'd have mouthpieces in, but we would legitimately spar."
The 60-year-old star admitted Tom was "jacked" at the time, whereas he wasn't quite as focused on working out.
"Tom is like this beast. And I hit him real clean and I rang his bell," he said.
"And the next thing I knew I woke up and I was coming to on the floor. He like completely knocked me out."
The West Wing star thinks the Mission: Impossible actor's defensive instincts kicked in after he "hit him hard and his eyes went black".
There was no hard feelings between the two, as Lowe jokingly compared their sparring sessions to David Fincher's 1999 film Fight Club.
11°C