You are a Mets fan and you were thinking the worst. Four batters into the game Steven Matz had allowed a three-run homer to Ryan Zimmerman. Seven innings done and the Mets had two hits.

The outs and innings were ebbing away and with it any lingering good vibrations from opening the season with 11 wins in 12 games. The three-game sweep in Washington earlier this month felt like something yellowed at the edges, as if Tom Seaver and Jerry Koosman and Jon Matlack pitched in it.

Were you cursing yet, Mets fans, that somehow you had got sucked in again? Were you figuring out the magic number for elimination, though no matter the outcome Wednesday night the Mets would still be in first place and 5 ¹/₂ months would still remain?

Three weeks ago, you Mets fans would have signed up for a 12-5 start to the season without qualm. Heck, you might have offered a relative or two in exchange. But now the Mets were about to fall to 12-5 and it felt more like an insult than a gift.

Not only were the Mets poised to be swept three games by the Nationals, but swept three games in which Max Scherzer and Stephen Strasburg did not start and Adam Eaton, Daniel Murphy and Anthony Rendon did not play. Swept three games that felt like mouth-to-mouth resuscitation on what had been a lifeless opening to the season by the division-favorite Nationals. The own-the-Mets-at-Citi-Field Nationals. This was the unpardonable married to the unforgivable — letting Washington up off the canvas.

Not again.

But as surely as the Mets bullpen squandered the series opener by allowing six runs in the eighth inning, the Nationals relief corps returned the favor — and then some — by yielding nine eighth-inning runs Wednesday night.

“It is just another win in the season when you look at it as a whole,” Mickey Callaway said after the Mets had finished off the Nationals 11-5. “But it was good for them to know we are never going to give up.”

Suddenly, 13-4 seemed a whole lot more than one game better than 12-5. It is amazing — or is that Amazin’? — how moods could fluctuate so much even in April. Part of this is the devilish hold the Nationals have held over the Mets, particularly at Citi Field. And part of it is the Mets’ tortured history of so often turning gold into garbage.

Who knows what a Wednesday night in mid-April will mean over the course of a long season. Was Game 17 seminal or just Game 17?

“We understand the implications of these games,” Michael Conforto said. “We feel we are the two teams atop this division and we didn’t play well against them last year [6-13, 2-8 in Flushing]. So, I do think it is big. It is a rivalry, chalk it up to that, this is a rivalry.”

Which is why this victory had that sense of both exhilaration and exorcism for the Mets. The Nats had won 51 of the past 70 at Citi Field and when Zimmerman, hitless in 11 at-bats against Matz to begin the game, made it 3-0, 52 out of 71 already was palpable.

The Mets closed to 3-2 in the fourth, one of the runs gifted when Zimmerman threw away a potential inning-ending double play. And Callaway lifted Matz, who had settled in to retire 10 straight, in what felt like fourth-inning panic — Callaway said it was because Matz had expended 33 pitches in the first, he was not long for the game anyway and he wanted to seize a scoring chance. But Amed Rosario rapped into a double play with the bases loaded and the Mets did not get another hit until the eighth.

In between boos came for Yoenis Cespedes and louder ones for Jose Reyes and mostly there was the constant murmur of unease and disenchantment that filled Citi Field.

And then the eighth.

The Mets entered down 4-2 and sent 12 men to the plate. Cespedes had a key single early in the inning and a grand slam later — both on 0-2 pitches. Todd Frazier tied it with a two-run single and Juan Lagares came off the bench for a vital two-run double.

“We went out and took it,” Callaway said.

But just imagine what not taking it would have felt like. Mets fans were living it for seven innings, the here-we-go-again churning in their brains, making stomachs queasy. The Mets were about to fall to a dispiriting 12-5.

Because it was the Nationals — even in mid-April — 13-4 just feels like a different world.