It was only one game, but it meant the world to the Mets. They knew it was going to tell them what kind of All-Star break they were going to have, what kind of first half they had played and basically what the status of their world is right now.

The answer to all of the above is “not as good as it could have been.” They lost to the NL East-leading Nationals, 3-2, on Sunday and fell back to where they had been after being swept in Washington the week before last: six games back and puzzled.

The game at Citi Field and the whole four-game series — of which they lost the last three — each felt like the one that got away.

Of course, it again revolved around the player who got away. Daniel Murphy hit yet another home run against his former team, a two-run shot off Steven Matz’s hanging curveball in the first inning, and the Mets never did get even. They got two home runs from Jose Reyes, another Met who got away before coming back this past week, but they left with a hill to climb.

“As I’ve said before, we were in this situation a year ago, where things looked bleak, and we ended up playing in the World Series,” Terry Collins said. “So we’re upbeat. We’ll take the rest and get ready for the second half.”

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Wilmer Flores said last year “gives us confidence.” Referring to the fact that the Mets are in good wild-card position, he added, “I don’t think we’re worried at all. We’re right in the mix. We’re right where we wanted to be.”

The Mets are 47-41, slightly better than they were at the break last year (47-42), but they are four games further out of the top spot. Plus, all sorts of things fell into place for them after the 2015 All-Star break: Their starting rotation remained mostly healthy, they acquired Yoenis Cespedes and, once they made the postseason, Murphy performed like the title character in “The Natural.”

He has not stopped, especially against the Mets. His home run off the facing of the second deck was his seventh against the Mets and gave him 21 RBIs in 13 games. “I’m just a small piece of it, but obviously I’m excited to help us win games,” said Murphy, who will play for Collins again Tuesday night in the All-Star Game.

Murphy has scorched the Mets, batting .423. The Nationals have won nine of 13 against them.

“I don’t think it’s just against us. He’s hitting like .350,” Matz said of the former teammate who leads the major leagues at .348. “He’s just a really good hitter. I don’t have any answer, otherwise I would not have given up a home run to him today.”

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Matz (7-5) actually was solid in his seven innings, aside from the mistake to Murphy and the two third-inning walks that set up Wilson Ramos’ run-scoring single. His left arm felt good, regardless of his elbow bone spur, and he retired Murphy twice.

The problem this time was that the Mets, bothered through the first half by a one-dimensional, homer-oriented attack, generated nothing other than Reyes’ two homers against Gio Gonzalez (5-8). They did nothing at all against Tanner Roark (a starter used in relief before the hiatus) and closer Jonathan Papelbon.

“Right now we don’t feel too good because we lost three out of four to the team who is in first place, but we have to put this series in the past,” Reyes said. “We know what happened to this team last year and we’re kind of in the same situation right now.”

In other words, it wasn’t the end of the world. “We’re ready. We’re confident. We believe in the talent that we have,” he said. “We didn’t finish the first half the way we wanted to. That’s baseball. Start the second half and go from there.”