NEW YORK -- Ever since Fred Wilpon first uttered the phrase 15 years ago, the idea of “meaningful games in September” has been a benchmark in Flushing. Only infrequently this decade have the Mets managed to reach the season’s final month still in contention -- most prominently in 2015, most recently in ’16, but not at all since.

When they swept the Indians at Citi Field just last week, that, improbably, seemed bound to change. At that point, the Mets had not only won five in a row, but 27 of 36 to turn a lost season into an intriguing one. All they needed to do was survive the Braves and Cubs to reach the final month in reasonable fighting shape.

October? That was never a guarantee. But September, at least, promised to be interesting.

The Mets then lost six straight games, capped on Thursday by a 4-1 defeat to the Cubs that felt a bit like an epitaph. Jacob deGrom allowed two home runs to Victor Caratini, including a go-ahead three-run shot in the seventh, and the Mets never recovered. They now stand five games back of Chicago for the second National League Wild Card spot with 29 to play. They also trail the Nationals, Phillies and Brewers. Their task is still not impossible, but verging toward it.

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“We’ve got to win,” deGrom said. “I think everybody knows that. It’s late in the season. We kind of dug ourselves out of a hole and put ourselves in a little one, so we’ve got to dig ourselves out again.”

Doing so, for the Mets, will now require something more than a strong month of play. To upend either the Nationals or Cubs, who hold the two NL Wild Card spots, the Mets will need to rip off a winning streak similar to the one they enjoyed earlier this month.

On the one hand, they know they can do it because they’ve done it before. On the other, asking for multiple miracles in a single season is not the soundest business strategy.

The Mets’ only run Thursday came via a J.D. Davis homer in the first inning off Jon Lester, who entered the night with an 8.51 ERA in August. If deGrom had designs on making that stand tall, Caratini squelched them with his solo shot in the second inning. From there, deGrom retired 15 straight Cubs until Amed Rosario bobbled Kris Bryant’s short-hop single in the seventh. Javier Baez followed with a soft hit and the next batter, Caratini, bashed another deGrom slider into the second deck in right.

deGrom wanted the pitch down and inside, diving toward Caratini’s back foot. It instead hung high, allowing Caratini to lift it.

“You’re like, ‘Oh, what just happened?’” Callaway said. “You look up and you’re like, ‘Oh man.’ But that’s just how this game goes.”

It is how things have gone all season for the Mets, save from one magical stretch from mid-July to mid-August. The final six games of a nine-game homestand against the Braves and Cubs could have cemented the Mets’ status as postseason contenders, but they lost all six. As a result, the Braves took a hammerlock on the division, while both the Nationals and Cubs positioned themselves as heavy favorites to earn Wild Card spots.

“Obviously, you want to play well, especially against the Cubs, who are right in front of us,” Jeff McNeil said. “It’s just real frustrating to let them do what they did to us.”

Offering the opposite perspective, Lester noted that “this whole series was huge for us,” lauding the Cubs for beating Marcus Stroman, Noah Syndergaard and deGrom in succession.

“Huge” isn’t a word used often in the Citi Field manager’s office. Before deGrom’s first pitch, Callaway refused to call this game, or any game, a must-win for the Mets. Players in the clubhouse offered a greater sense of urgency, understanding the extent to which the season seemed to be slipping away from them. As recently as Aug. 22, the Mets had a better-than-even chance to make the playoffs, according to FanGraphs’ projection system. By Thursday night, that number had fallen to 13.6 percent.

September is only three days away. The Mets may yet reach it with a chance to play meaningful games, but only if their free fall ends in a hurry.

“You come in and you know that you’re playing them head to head, you know where everybody’s at, and you want to go win the series so you can create your own destiny,” Callaway said. “It didn’t work out.”