9:22 AM PT -- A spokesperson for the San Diego Police Department tells TMZ Sports authorities at the game did take an incident report and both parties were ejected ... although neither man said they wanted to press charges and no arrests were made.

"Medical attention was declined by both subjects," cops added.

A pair of MLB fans hit the ballpark Tuesday night to catch a baseball game, but at some point, they found themselves in the middle of a boxing match -- and the violent scene was all captured on video.

The impromptu fistfight happened during the Padres vs. Twins tilt at PETCO Park in San Diego ... when a man in a white tank top and a dude in an all-black 'fit decided to throw hands at each other.

Initially, the guy with the upper ground seemed to be fairing well -- as he dodged multiple punches ... all while talking some smack.

But then the dude in the black tee unloaded a flurry of fists that tagged his opponent repeatedly.

Following the series of combos, you can see the man ate the blows so hard, he was left with a bloody mouth.

No word on if the altercation ended in any arrests -- we've reached out to cops for comment, but so far, we've yet to hear back.

As for the action on the field ... the fighters missed a good one while they were duking it out -- as the Padres beat the Twins, 7-5, in a game that featured six total runs in the eighth inning.