How long has it been since the Mets last faced the Dodgers?

So long that the last time the teams played each other, “OMG” and Grimace were just an acronym and a fast food fictional character.

It would have been hard to imagine then, in late May, that the National League Championship Series still lay ahead for both.

The Dodgers, yes, but the Mets?

That’s baseball.

The NL pennant will be decided starting Sunday with Game 1 of the NLCS between the Mets and Dodgers in Los Angeles.

The Dodgers joined the Mets in the NLCS round on Friday with a 2-0 victory over the Padres in Game 5 of the NLDS.

It’s those Dodgers who won three games at Citi Field in May, sending the Mets 11 games under .500 and leading to changes.

The Mets held a players meeting.

Jose Iglesias arrived to reinvigorate the lineup, bringing his recently released song “OMG” to become the soul of the team.

And after Grimace threw out the ceremonial first pitch on June 12 and the team continued to win, an unofficial team mascot was born.

It will be the fourth postseason series between the coastal rivals.

The Mets won the last one, the 2015 NLDS, on the back of Daniel Murphy.

The only NLCS meeting between the teams came in 1988, when the Dodgers surprised a Mets team that had visions of winning a second World Series in three years.

Now the names are Shohei Ohtani, Mookie Betts, Freddie Freeman and Yoshinobu Yamamoto and enough star power to keep Southern California shining during a blackout.

After weeks of scrambling, the Mets found themselves in the unfamiliar position Friday of taking it relatively easy while their opponent faced the stress in the next round.

The Mets held an afternoon team workout at Citi Field before the Padres and Dodgers played Game 5 of the NLDS in Los Angeles.