Before the Blues Brothers, before being cast on Saturday Night Live, John Belushi was part of National Lampoon's Lemmings comedy troupe. It was here where John perfected his dead-on mimic of singer Joe Cocker, which led to a 1-time-only duet with Cocker on SNL 3 years later.
Here, Belushi, impersonating Cocker, performs "Lonely at the Bottom", from a Lemmings Roadshow, back in 1973, 2 years before SNL. And, yes, that is Chevy Chase on the drums. Chase had played with a pre-Steely Dan Walter Becker & Donald Fagen before turning to comedy.