Pro wrestling legend Sting is hanging up his boots after Sunday's big match at AEW Revolution ... a moment so special, tag team partner Darby Allin says it's actually the highlight of his young, but impressive, career -- and he's not even the dude retiring!

"Oh, without a doubt. Without a doubt, it's the biggest [match of my career]," Allen told us, adding, "He's been around longer than I've been alive. Like on top of the wrestling. It's really cool to be a part of it and definitely my biggest match and I'm not taking anything for granted. I'm so grateful for this opportunity, and I'll stop at nothing to prove my loyalty."

Of course, Sting is one of the most legendary wrestlers of all time. Period. WCW, TNA, WWE, and now AEW ... Sting was the man in all the top promotions. He's a WWE and TNA Hall of Famer. He's also won just about every title under the sun.

Wrestling fans have been anticipating the match ... Sting and Darby are fighting The Young Bucks, Matthew and Nicholas Jackson Sunday night in Greensboro, NC.

"I try not to make it about myself at all. I just want to make sure this man's career ends with the respect it deserves, and it's cool to be a part of the end," Darby said of the meaningfulness of the moment.

"I feel like the biggest part of a wrestler's career is the end. If you s*** the bed in the end, people are always gonna remember that. 'Aw, he should've hung up his boots years ago.' But I convinced Sting to come back and wrestle, so I feel it's my duty to make sure that he doesn't embarrass himself."