What if David Fincher directed “Rocky”? It might look something like “Rocky” the musical.

That was part of the concept, anyway, for Alex Timbers, the director of the spectacularly staged new Broadway tuner that opened March 13. “I knew I wanted it to be cinematic,” he said at the opening night afterparty at Roseland Ballroom. “I wanted it to look like a David Fincher film.”

There were hefty challenges in getting the laconic “Rocky” to sing. Lyricist Lynn Ahrens found herself faced with a group of characters who don’t have big vocabularies, and she said it was tough to stay true to that.

But there were rewards, too: “I got to use my first double negative in a lyric!”

Standing out among the theater types taking their bows that night: Sylvester Stallone himself, the writer and star of the Oscar-winning film that inspired the musical.

At the opening night party, Sly said he felt like a proud parent. And he had came to the realization that all theater people have at one point or another: Broadway ain’t for sissies.

“I’m exhausted,” he said with a laugh. “I feel like I’ve gone 15 rounds!”

(Pictured: Burt Young and Sylvester Stallone at the Broadway opening of “Rocky”)