The Mets' Yoenis Cespedes celebrates with Michael Conforto after Conforto...

The Mets' Yoenis Cespedes celebrates with Michael Conforto after Conforto hit a two-run homer during the fifth inning against the Nationals at Nationals Park on Thursday. Credit: AP / Alex Brandon

WASHINGTON — The story of the Mets’ season starts off with one primary antagonist: the Nationals, the team with the consecutive division titles, the generational player and free agent to be, the pair of aces, the former Met turned Met-crusher.

The Nats owned the Mets last year, and the year before, and the Mets getting to where they want to go in 2018 likely will require a dramatic reversal of those fortunes.

And for at least a day, the Mets were better. Much better.

They spoiled the Nationals’ home opener Thursday with an 8-2 win in which they received noteworthy contributions from every area of the roster. Jay Bruce’s seventh-inning grand slam turned it into a blowout, Michael Conforto and Yoenis Cespedes also homered, and the bullpen continued its early-season dominance as the Mets improved to 5-1.

That this one came against the Nationals made it even sweeter for them.

“We all know the importance of it,” Conforto said. “They’re a great team. We’re a great team as well. You say, ‘Take every game like it’s the same,’ but I think there is something different when we come here to play and when they come to [New York]. It’s a rivalry, and it’s one that we want to come out on top of.”

The Mets came out on top this time thanks to sticktoitiveness early and timely hitting late.

They answered Washington runs in the first and third with runs in the second and fourth. Conforto, in his first game since last August, homered in the fifth off Stephen Strasburg to give the Mets a 4-2 lead. Bruce, who fell behind 0-and-2 before working a full count, all but put the game out of reach with a grand slam off Brandon Kintzler in the seventh.

Jacob deGrom’s outing was much like his first one: good enough, but not as dominant as he can be (especially during the day and especially at Nationals Park; he entered the game with a 1.98 ERA in day games and a 2.95 ERA in Washington). DeGrom allowed two runs (one earned), four hits and three walks in six innings, striking out five.

Jerry Blevins, Robert Gsellman, Hansel Robles and Seth Lugo combined to strike out six and allow two baserunners in three shutout innings. The relievers checked the final box of what has become the Mets’ template in their early success: a little bit of everything from everyone. The offense was good, the starting pitching was good and the bullpen was even better.

The Mets even had a big at-bat from a pinch hitter. Brandon Nimmo, forced to the bench by Conforto’s return, doubled with one out in the seventh when he hit for deGrom. That started the rally that ended with Bruce’s grand slam.

“Everybody is in a really good spot confidence-wise,” manager Mickey Callaway said. “They’re playing the game the right way. It’s just fun to see. The pitchers are going out and attacking. Hitters are putting together great at-bats, being smart on the bases. That’s the way you win ballgames.”

The Mets, who are 3-9-1 in their past 13 series against the Nationals, are in a good spot to win this one. The teams will play 18 more times, and you can bet the season series will loom large in the year-end standings.

“I think [this series] is important. I don’t think it’s necessarily imperative,” Bruce said. “But any time you can come in and beat a team of this caliber is huge.

“We understand it’s going to be like this all year. There’s going to be big series. I hope to continue playing in them and them mean something every time we play. Everyone in here’s goal is to be playing meaningful baseball in September. If we’re going to do that, we got to beat these guys.”

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