The Blake Lively and Justin Baldoni beef is going big time ... getting roasted during the opening monologue at the Critics Choice Awards.

Chelsea Handler is hosting tonight's award show at the Barker Hangar in Santa Monica and she poked fun of the "It Ends With Us" costars and their legal war.

The comedian started by thanking Blake and Justin for providing a distraction for lots of folks who have had a tough start to their year.

Chelsea built up and then dropped her zinger ... saying it doesn't matter whose side you take, Blake or Justin's, we all know how this is going to end ... without a sequel.

Hollywood's been captivated by the Blake and Baldoni case ... which is now moving from the court of public opinion to a courthouse in New York.

It's certified pop culture now ... when you get made fun of at award shows, you know you've done something big.