Mikey Garcia -- the king at 140 -- says he's willing to go up in weight for a shot at a superfight with Errol Spence ... and he wants it bad!
The reigning WBC light welterweight champ tells TMZ Sports he's already trying to set up fights AFTER his brawl with Robert Easter on July 28 ... and he's got his sights set on Spence.
"I'd really like an opportunity to fight Errol Spence," Garcia said ... "Let's get together after this fight. Maybe we can work something out."
Garcia -- who's fighting at 135 next weekend -- says he'd even go up to 147 to fight Spence.
If Garcia beats Spence at 147 ... he'd have belts in 4 weight classes at the SAME TIME.
Let's do this!!!