The actor plays attorney Mick Maller in the new drama about a supposedly easy case defending Ryan's Playboy character Louis Roulet on murder and rape charges.
However, he then discovers it is a much more complex situation, leading to a power struggle between the two men.
Matthew and Ryan wanted their characters' skirmishes to be as real as possible, so avoided running through their scenes before filming in order to make unexpected plays on one another.
Matthew explained: "I've done films where we don't rehearse and I've done films where we heavily rehearse. I like rehearsals. Just for this particular relationship that my character, Mick, has with Roulet, my client.
"We're both trying to play each other, throughout the movie. I didn't want to know. I didn't even want to have an idea of what his hand was going to be, and I sure as hell didn't want to share with him what my hand would be.
"I was like, 'Let's meet when we're in the scene. Let's meet each other there and go on this two-month, fun Journey of getting to know each other through our characters.' "
Matthew also revealed he particularly enjoyed playing a lawyer because it was originally his chosen career path - until he realised how long the training would take.
He admitted to Collider.com: "When I was in school, that's where I thought I was heading - law school at the University of Texas. I changed my mind my junior year, when I looked up and saw two more years of school, then four years of law school. I thought, 'You'll be 28 by the time you get out and you can actually implement an imprint in society.' I didn't like that idea.
"Now, I'm glad that I changed my path. I get to do this, and then go on to another story."