The actor/director gave his thanks to RDJ in a new Esquire interview profiling the recent Oscar winner -- and he detailed how Rob was one of the only A-listers back in the day who were willing to give him a second chance

MG says, "One time, I got into a bit of a sticky situation where it kind of ended my career. I was drunk in the back of a police car and I said some stupid s**t, and all of a sudden: blacklisted. I’m the poster boy for canceled."

Mel continues, "A couple of years into that he invited me to some kind of award he was getting -- we always had this kind of seesaw thing, where if he was on the wagon, I was falling off ... So I was pretty much nonexistent in Hollywood at the time, and he stood up and spoke for me. It was a bold and generous and kind gesture. I loved him for that."

He's referring to Rob speaking at an award show in 2011 ... during which, he explicitly defended Gibson -- and said nobody in Hollywood was without sin ... and asked for folks to forgive Mel. It was heartfelt ... and MG certainly seemed to appreciate it at the time.

While it's hard to say if Gibson was ever back in the swing of things the way he was pre-2006 -- he appreciates Rob sticking up for him regardless ... crediting him for reviving his shine in H'wood. Mel's acted in several films since, and even directed an Oscar darling from 2016.