Ryan Reynolds made a surprise appearance at Radio City Music Hall on Friday night to support Hugh Jackman ... while the legal battle between Blake Lively and Justin Baldoni has escalated severely.

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RR honored his Marvel costar and best mate at the opening night of Hugh's one-man show "From New York, With Love" ... offering a combination of ball-breaking and deep admiration for his fellow actor.

The few minutes were sweet and moving ... but odds are the war between RR's wife and Baldoni was on audience members' minds -- as that got even uglier this week ... and it looks to get worse.

As TMZ previously reported ... After Blake initially sued Justin, Ryan was roped into the legal drama when Justin responded with his own lawsuit -- Baldoni even claimed Ryan mocked him with his "Nicepool" character in Ryan and Hugh's blockbuster "Deadpool & Wolverine."

Baldoni's also claimed in a $400 million lawsuit Ryan and Taylor Swift pressured Baldoni into taking Blake's rewrite notes of the film's script into account.

Just this week, Baldoni's team released behind-the-scenes footage in an effort to show Blake's accusations of sexual harassment were false ... while Blake's side said the move backfired, as it showed just how inappropriate Justin behaved on the "End with Us" set.

But, Friday night was to celebrate and honor Ryan's BFF, which RR did with a few jabs ... but also with a deep love for "the first major movie star I ever worked with."

Needless to say ... HJ made sure to return the love, during what was the first of 24 performances over eight weekends this year.

Guess it's true what they say ... friends make everything better.