There was something so definitive about Daniel Murphy’s majestic blast in the first inning Sunday night — the towering, soul-crushing home run that some fans had to watch on TVs while they were still getting their Shake Shack burgers or finding their way to their seats.

You could really use a bat like mine right about now, it seemed to say. Or, did you really think that this duct-tape lineup — the result of a clubhouse that’s more triage center than locker room — could really match up against the first-place Nationals? Against Max Scherzer? Is Jose Reyes, hitting sixth and batting .104, going to save you? Is Kevin Plawecki?

Things are dark at Citi Field these days, and no matter how much Terry Collins tries to stay positive, the hard truth is that the Mets were swept by the Nationals, 6-3. They’ve lost eight of their last nine and have been outscored 37-21 in those losses.

“Any time you get swept, especially a division opponent, it’s no fun,” said Neil Walker, whose two-run homer in the third drew the Mets within 4-3. “More than anything, you try not to freak out. That’s absolutely the worst thing you can do 20 games into the season. Nobody is freaking out in there. People might be freaking out outside of here, but that’s none of our concern.”

Be that as it may, that’s a whole lot of instances of the phrase “freak out” in this, the last week of April. But really, who can blame the Mets (8-11) for being a little weary?

Yoenis Cespedes was available to pinch hit but still is nursing an ailing hamstring. He declined to speak to the media, saying through a spokesman that he wanted to wait until tomorrow to see how he feels. Lucas Duda and Wilmer Flores are on the disabled list, though Duda said he feels significantly better. The team essentially is playing with half of an Asdrubal Cabrera, who’s trying to tough out a hamstring injury. Travis d’Arnaud might be DL-bound if he’s not better by tomorrow.

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The list is so long, and so sad, that you wonder if Collins just says it over and over in his sleep.

“I think the concern is, are we going to get these guys back?” he said. “The concern is to get healthy, because once we get healthy, I think things will turn around. I don’t think we lack confidence.”

If there is a positive — and it can be nigh impossible to find one these days — it’s that the Mets have learned a thing or two during the last few years. For one thing, they know how to scrap. Last season, when they lost Cespedes to injury along with three-fifths of their rotation, they stayed afloat well enough to make it to the wild-card game. This season, the injuries have come early enough that they shouldn’t cause permanent damage. And, much like last year, the Mets are learning what they have when the big names aren’t around.

Take Michael Conforto, for instance. Having claimed leftfield in Cespedes’ absence, he’s shown that he has what it takes to be an everyday player.

Does he still struggle against lefties? Indubitably. Can the Mets deal with it now that he’s made something of a habit of hitting leadoff home runs? You better believe it.

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On Sunday night, he blasted off on Scherzer’s second pitch, slapping a 94-mph fastball off the leftfield foul pole for his fourth homer and second to lead off a game.

Two innings later, with the Mets down by three, Walker made good on Collins’ bloop-blast philosophy. Conforto singled and, two outs later, Walker hit a two-run shot to right. It didn’t give the Mets the lead, but it sure gave them hope.

That hope faded in the eighth, when Ryan Zimmerman hit a two-run second-decker off Josh Smoker.

But that’s how it is these days. Every good thing is followed by a significantly greater bad thing. The Mets’ only hope lies not in Murphy’s Law but the Law of Averages. Eventually, Collins said, things have to level out.

“Someplace, there’s a nine-game winning streak coming up,” he said. “That’s how good this team can be. I do believe we have the ability to take off. If you win nine, 10, especially this time of year, you’re back in it. Every team goes through a bad streak. All you gotta do is say hey, this is ours, and when we’re done, we’re going to get back in this hunt.”