Star-Lord is coming to Boston ... because Chris Pratt says he's ready and willing to PAY UP in his Super Bowl bet with Chris Evans. 

You know the back story, Pratt's a huge Seahawks fan. Evans loves the Pats. 

They had made a wager on the game ... Evans lost, he'd have to show up to a Seattle children's hospital dressed up as Captain America. 

If Pratt lost, Star-Lord has to show up at Evans' non-profit housing venture "Christopher's Haven."

Well, good news for both sides ... because after the game Pratt tweeted, "Congrats to the world champions @patriots you were the better team tonight. I will be visiting @chris_haven as Starlord."

And Evans ... you don't think Captain America's gonna leave a children's hospital hangin' do ya?

"Thank you to @prattprattpratt for being a good sport. I'll be there with you at @chris_haven, and don't worry @seattlechildren, we'll be coming there too!"

However, Evans did add one last shot ... 

"And lastly, I don't think anyone can ever doubt the mental toughness of Tom Brady. Tough couple weeks, but he showed why he's the greatest of all time. #PSIdonthearyounow #anyballanytime."