Jimmy Fallon -- Kanyes Stephen Colbert's Emmy Speech

Jimmy Fallon just hijacked Stephen Colbert's Emmy awards acceptance speech -- and it was either the first shot in a new late night war ... or a totally planned bit.

Colbert's crew won for 'Outstanding Writing in a Variety Series' ... and after Gwen Stefani butchered Colbert's name, Fallon ran up on stage trying to deliver his own acceptance speech.

Colbert's reaction is pretty funny -- especially considering he's taking over for David Letterman on CBS when he retires ... and he'll be battling Fallon for ratings.