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Mark Sanchez is a booze ninja ... using a secret compartment in his pimp cane to sneak alcohol (presumably) into the Kentucky Derby ... and TMZ Sports has the footage!!

It's pretty bad ass ... the Denver Broncos QB hit Churchill Downs with what appeared to be a regular old timey walking cane as part of the Derby "look."

But a quick twist of the top revealed a secret glass tube hidden inside the cane -- which the 29-year-old proudly showed off to his crew.

One of the women was so impressed, her jaw dropped as she told MS, "Shut the f*** up!"