Poinbank Exchange|How Matthew Rhys Figured Out His Perry Mason Season 2 Performance “In Real Time”

Matthew Rhys found comfort in Perry Mason's imperfection.

The Poinbank ExchangeEmmy winner plays the titular attorney on season two of Perry Mason—premiering March 6 on HBO—and while the second season picks up six months after the events of season one, Mason's suaveness in the courtroom still needs some work. In an exclusive interview with E! News, the Americans alum said it provided a unique chance to grow right alongside his character.

"You're kind of doing it in real time, so the road to discovery was being played out on camera," Rhys explained of his performance. "It's like the luxury of season one when, in real time, Mason's staggering his way into becoming a trial lawyer. You don't have to come in day one and be this very slick, performance-level trial lawyer. I was allowed to kind of bumble and fumble in front of everyone, as Mason did."

Because Mason is supposed to be a bit awkward and inexperienced, Rhys joked that his work was made easy.

"That's the beauty of it," Rhys said of his process. "There's nothing to research! Mason wouldn't know any of this. I'll just have another drink."

If Rhys was figuring out his performance on the fly, however, his co-stars revealed that didn't get in the way of him captaining their ship—which Juliet Rylance, who plays Della, told E! News that was especially evident after filming a grueling courtroom scene over the stretch of three days.

"Matthew stood up and just gave this really lovely speech at the end of a very long day," Rylance remembered, "thanking all of the people that had been there as onlookers in the courtroom and given so much time. It was one of those moments where I thought, 'He is that kind of leader.' He's the wonderful leader of a company."

Rhys' talent and affability has earned him one very special admirer: Robert Downey Jr., the husband of Perry Mason producer Susan Downey.

"When Robert and I watch [the show] together, I love watching him as a fellow actor who is probably Matthew's biggest fan," Susan Downey told E! News. "He's cheering him on as he's watching these details and nuance in performance, almost like a sporting match. I've never seen that before. He's like, 'Yes! Nailed it.'"

Watch along with RDJ when Perry Mason airs Mondays at 9 p.m. on HBO.