Los Angeles secured its 11th division title in 12 seasons after a 7-2 win over the San Diego Padres ... and after taking some family selfies with Mamiko and Decoy, it was time to take an alcohol shower with the squad.

It was the first locker room celebration of Ohtani's career -- he never sniffed the postseason during his six seasons with the Angels -- so naturally, he committed a party foul by not sporting protective goggles for the boozy bash.

Ohtani told reporters his eyes stung a bit as a result ... but he didn't seem to mind, as he said he hopes to pop even more bottles of champagne in the future.

Dodgers manager Dave Roberts even joked Ohtani's going to "smell like a brewery for the next week" ... but that celebratory cologne is exactly what he signed up for when he joined the franchise this past offseason.

It's been a heckuva campaign for the $700 million man -- he became the first player to ever hit 50 homers and steal 50 bases in a season ... and now he'll get to make his October debut.