Sylvester Stallone admits he was nervous working with this Hollywood legend for first time

Sylvester Stallone isn't afraid of much, but going head-to-head with this Hollywood star on screen made the "Rocky" legend sweat.

In a candid interview, Stallone admitted he felt the heat when Samuel L. Jackson signed on to join Season 3 of "Tulsa King."

"When I heard that was gonna happen, I went, 'Oh, this is gonna be a fist fight. This is gonna be a battle,'" Stallone told People. "Like two boxers in a ring, and who is gonna throw the first punch? So you're getting nervous because you're dealing with serious competition."

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Stallone, 79, leads the series as Dwight "The General" Manfredi, a mafia capo exiled to Tulsa. Jackson, 76, joins the cast as ex-con Russell Lee Washington Jr., setting the stage for a heavyweight face-off between two icons.

Instead of a showdown, Stallone said what he got was synergy.

"Once he walks in, he goes, 'Hey, dude brother,' and I went, 'Oh, here it goes.' But now we're good. Now we're flowing," Stallone shared. "We could do a show called 'Tulsa King and Buddy.' We just worked that well together."

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Despite the two sharing the same zip code for decades, they had never worked together - or even really crossed paths.

"We lived about a hundred yards away from each other for almost 30 years," Stallone revealed. "Yet we didn't - you know, we're always working. So, we never really saw each other, except at Planet Hollywood-type things or openings."

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While their careers took different routes, both actors seem to have landed in the same place now, looking for roles with deeper meaning.

"I guess he got to the point that I did that he's done pretty much everything," Stallone said. "But at this age in life, you want to be a little bit more grounded, steady, have your own show so you develop this thing, really flesh it out instead of working someplace for 10 days or a gig here and there."

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And though "Tulsa King" is the latest win in a legendary career, Stallone admitted he still looks back on his rise to fame with a sense of disbelief and some regret.

"That journey - I wish I had been more aware," he reflected. "But you're just trying to survive. You're not even aware of the chaos around it, because I said, 'I've got to do this.' I told myself, 'You're probably not going to make it, but I don't want you to have any damn regrets. You have to go 100%, not 99.'"

Fox News Digital has reached out to reps for Stallone and Jackson.