Chris Pratt -- Pays Tribute to Lil Sebastian ... At 'Parks and Rec' Party

Chris Pratt gave an emotional performance Saturday at the wrap party for "Parks and Recreation" ... all to pay tribute to one of Pawnee's finest treasures -- Lil Sebastian.

There was no hologram horse -- but Pratt belted out the Mouse Rat song "5,000 Candles in the Wind" with Ron freaking Swanson playing the guitar ... and just like you'd expect, it was awesome!

Everyone in attendance was stoked -- and since the show finished filming it's final season this week ... it will probably be the last time anyone hears it in person.

Treat yo self ... and watch the video.