Jack Black and James Marsden -- We Bullride LIKE CHAMPS! (VIDEO)

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Jack Black and James Marsden might not be hot chicks in tight white tops -- but they can still ride the hell out of a mechanical bull ... and TMZ has the awesome footage that proves it.

Black and Marsden -- who are filming a comedy right now -- hit up the popular Saddle Ranch Saturday night on the Sunset Strip, and each hopped on the bull for pretty lengthy rides ... we're talking well over 8 seconds.

In the video, Jack even busts out a few tricks before taking a funny spill to end his ride -- and James wraps his legs so tightly around the bull ... he manages to go no-hands!

No city-slickers here.