Tina Fey and Amy Poehler 's revived 'SNL' "Weekend Update" was one of the big treats at the Emmy Awards ... and proof positive competing networks can work together with great results.

Sources with direct knowledge tell TMZ the Emmys producers over at Fox approached the "Saturday Night Live" peeps at NBC to discuss a legacy revival segment -- and both parties decided having Tina and Amy reunite in their old 'Weekend Update' roles would be awesome.

If ya missed it, they pulled it off while presenting the Emmy award for Live Variety Special. We're told both networks wanted Amy and Tina to do it -- not only because of their 'SNL' chops -- but, also because they've teamed up for so many live entertainment gigs over the years.

As for the possibility they have an official reunion on an episode of 'SNL' -- one source says there's no immediate plans.