5:00 PM PT -- Blake and Ryan kept their fun weekend going on Sunday ... stopping by "SNL50" to show love for the sketch comedy show they've both previously hosted.

Blake Lively and Ryan Reynolds might be in the middle of some legal drama, but they're still finding time to celebrate ... showing up to Chris Rock's birthday party and taking a pic with a controversial comic actor.

The A-list couple hit the Crane Club in New York City Saturday night to celebrate Rock's 60th with a bunch of other stars connected to "Saturday Night Live."

The two ran into Chevy Chase at some point clearly ... 'cause he posted a photo where he's smack dab in the middle of the two stars.

Check out the pic ... everyone's grinning from ear-to-ear -- with no indication of the couple's current legal troubles.

As you know ... Blake and Ryan have been engaged in a legal struggle with Justin Baldoni since late December -- when Lively accused the actor-director of sexual harassment and taking part in an organized smear campaign against her.

Baldoni sued the couple for $400 million last month ... and, he's claimed they worked in concert with the New York Times to take him down.

Most recently, Lively subpoenaed Baldoni and his publicists for phone "receipts" ... basically looking for evidence to back her claims of the smear campaign.

Baldoni's attorney Bryan Freedman told us, "Subpoenas are an ordinary part of the litigation process. What is extraordinary is what the Lively Parties are seeking. They are asking for every single call, text, data log, and even real-time location information for the past 2.5 years, regardless of the sender, recipient, or subject matter. This massive fishing expedition demonstrates that they are desperately seeking any factual basis for their provably false claims. They will find none."

BTW ... Baldoni isn't sweating the legal battle either -- 'cause he was recently spotted surfing in Hawaii, looking super calm.