Time doesn't heal all wounds ... more than 3 1/2 years after fighting, Sean O'Malley still ain't fond of Marlon Vera (and the feeling's mutual), with the reigning champ telling TMZ Sports he's going to render Chito unconscious!

We talked to 29-year-old "Suga" just days before he heads to Miami for the main event fight against his 31-year-old rival ... about everything from the effect of his only loss (Vera injured O'Malley during the fight) to if he'll chase double champ status against Ilia Topuria.

On the August 2020 fight -- which Sean lost by TKO late in the first round -- O'Malley had this to say:

"I got a lot of hate for saying mentally I didn't lose that fight. I didn't feel like my skills were beat. It was a freak accident. Yeah, he threw the kid. Yeah, blah, blah, blah, blah, blah. I've heard it all. Mentally undefeated, going in there with that mindset. Going in there with the mindset to kill this dude, and it's as simple as that," Suga told us.

We asked O'Malley, brevity of the fight aside, if he could take away anything from the first outing.

"Not really," he added. "Like you said, it was such a short fight, there really wasn't too much to take away from it. I was confident. I felt very confident in there. Even with the injury, my foot was shut off and I was still piecing him up. Dotting him up, chasing him down. I'm just very confident going into this fight."

It's Sean's first fight as defending champion ... we asked what, if anything, was unique this time around.

"Nothing's been different. My second 5 round training champ. Obviously, that last fight didn't go 5 rounds, it only went 2, 1 1/2. Nothing's really been different other than Chito, big fight, rematch. Same s***, different day. I've been doing this for 13 years."

Speaking of his belt, Sean won it with a masterful performance against Aljamain Sterling at TD Garden in Boston at UFC 292 in August 2023 ... in front of a decidedly pro-O'Malley crowd.

299 isn't in Beantown ... instead, the March 9 event will take place in sunny Miami, a city with a large Ecuadorian population. Chito was born in Chone, Ecuador.