OAKLAND, Calif. — Pete Alonso wasn’t subtle in setting the Mets’ single-season RBI record on Sunday.

There was his no-doubt home run in the fourth inning that gave him the record, but Alonso kept going, banging a shot off the right-field fence with the bases loaded in the eighth.

A huge Alonso day and road trip was complete in a 13-4 demolition of the Athletics at RingCentral Coliseum that gave the Mets an 18th victory in a rubber game this season to establish a club record. The Mets are 18-4 in such games.

Atlanta’s victory in Philadelphia meant the Mets boarded their charter flight home leading the Braves by 1 ½ games in the NL East. Atlanta plays in Washington on Monday and the Mets are off before beginning a two-game series against Miami at Citi Field.

Alonso finished 4-for-5 and with his five RBIs and increased his total this season to 128, four more than the previous Mets record shared by Mike Piazza and David Wright.

“It’s a huge honor,” Alonso said. “But I wouldn’t be in this position without my teammates. All year they have been putting together unbelievable at-bats. I feel blessed and honored to have the record, but without them I wouldn’t have got it done.”

Though the RBI doesn’t hold as much clout as it once did as a statistic, Alonso considers it important.

“They mean a lot because it’s a run-scoring competition,” Alonso said. “Getting hits is great for a personal stat, but I think driving guys in is important because the whole point of the game is to score more runs than the other team. I feel like that’s why we play, to see who can score the most runs.”

Alonso finished with four homers in six games on the road trip. In September he has blasted eight homers and driven in 23 runs.

“Some guys are collision hitters and he’s a guy when he collides with the ball it’s fun to figure out where it’s going to land,” manager Buck Showalter said. “There were a lot of great at-bats to get to that point and our guys, I’m so proud of their focus today in trying to win another series and get back home.”

The run support was plenty for Max Scherzer, who extended to 90 pitches in his second start back from the injured list and allowed one earned run four hits and one walk with seven strikeouts over six innings. In his return from an oblique irritation last Monday, he retired all 18 batters he faced in Milwaukee, departing after 68 pitches.

Facing a left-handed starting pitcher for a third straight game, the Mets jumped on JP Sears early, receiving an RBI single from Tyler Naquin in the second inning for their first run. In the third, Eduardo Escobar delivered a two-run single that extended the lead to 3-0. The Mets had loaded the bases on walks to Brandon Nimmo and Jeff McNeil with a Francisco Lindor single sandwiched in-between.

The Mets broke it open in the fourth with a two-out rally that needed four runs and a 7-0 lead. Lindor stroked a two-run double in the inning before Alonso launched a monstrous home run to left field. Alonso’s homer was his 39th this season, second in the National League to Kyle Schwarber (42).

“[Alonso] is just doing so much for our ballclub on and off the field,” Scherzer said. “He plays with so much heart and I think that is the thing people don’t understand is how he plays this game with so much heart. He’s been a treat to have as a teammate.”

The Mets established a season high with 19 hits. Francisco Lindor and Eduardo Escobar were both 3-for-5. Lindor finished with three RBIs and Escobar with two.

Seth Lugo surrendered a three-run homer in the ninth to Conner Capel after Adam Ottavino and Drew Smith each pitched a scoreless inning in relief.

Showalter had talked pregame of the need to find work for Edwin Diaz, who hadn’t pitched since Tuesday, but the Mets closer did not appear in the game.