Don Mattingly & Mustache REUNITED -- Legendary Lip Warmer Returns

... and all was right with the world again.

Thanks to the good work of Jimmy Fallon, Don Mattingly was reunited with his legendary lip warmer last night ... and it was magical.

Of course, Mattingly's mustache was like Samson's locks -- powering the former Yankees star into superstardom back in the '80s.

For some crazy unknown reason, Donny Baseball separated from his snot mop a few years ago ... and like Alex Trebek, he's never been the same since.