Timothée Chalamet clearly doesn't have a playoff superstition when it comes to his hair ... because he got a cut and shaved off his beard in the middle of the New York Knicks' playoff run.

The actor and diehard Knicks fans sat on celebrity row at Madison Square Garden Tuesday night to watch his favorite team complete a stunning comeback victory over the Cleveland Cavaliers ... but the Knicks weren't the only ones making a comeback -- Clean Cut Chalamet is back.

Check it out ... Timmy's hair is noticeably shorter and he's shaved off his thin mustache -- a transformation for the star many online are saying makes him look much younger than his 30 years.

While he got the fresh cut, it's not because he wanted to look good for Kylie Jenner necessarily ... because she didn't make it to this game -- she's actually hanging out on the West Coast at the moment.

With the Knicks big victory in Game 1 of the Eastern Conference finals, we're thinking Chalamet's new do may just be the good luck charm the Knicks need to break their championship drought!