Nothing worse than getting taken down in a ghost town.

The Mets’ postseason chances can die officially on Tuesday night with the right combination of results — Mets loss, Nationals win (they play two) and Brewers win — and if Monday serves as any indication, it looks like the memorial won’t be well attended.

The Mets face more than a talent gap in order to get to where they want to go. Their credibility gap with their fan base remains too legit to quit.

A generally funereal Citi Field hosted the Mets’ 8-4 loss to the lowly Marlins, kicking off this season-ending homestand on the wrong note. At 81-75, the Mets now trail the Brewers (86-70) by five games, with six contests left on the schedule, in the race for the National League’s second wild-card spot; the Nats (86-69), after defeating the Phillies on Monday, hold the top wild-card slot, five and a half games ahead of the Mets.

“Our backs are against the wall,” Mickey Callaway acknowledged.

Who has their backs, though? The Mets announced their tickets sold as 21,189, and while that didn’t appear to be an egregious overstatement of the folks on site — my Post colleague Mike Puma, who possesses a knack for crowd estimates, went with 15,000 — that’s not much of a showing for a team still mathematically alive in the season’s final week. The outfield seats in particular looked more sparse than a screening of “The Goldfinch.”

Which prompts the question: How meaningful is a “meaningful game,” to steal Fred Wilpon’s spoken ambition from long ago, if only the die-hards find meaning in it? Even if they didn’t believe in the Mets’ remote chance of reaching October, Pete Alonso’s quest to tie and surpass Aaron Judge’s rookie home-run record — he didn’t go deep on Monday, leaving him two behind Judge’s mark of 52 — didn’t do much for folks?

The quietude stood out all the more because of the fun atmosphere that had returned to Citi thanks to the Mets’ post-All-Star-break surge back into contention. For the season, the Mets’ per-game average of 30,501 marks an increase of 3,027 per game from last year, the third-best rise in the entire industry (thanks, Baseball-Reference). Clearly this group, headed by Alonso, has connected with the customers.

Alas, school started, the Giants found a quarterback and apparently people didn’t buy in on either the team’s slim odds or Alonso’s quite decent chance of success. Hence here we sat, with plenty of legroom for all.

Oh, the folks here occasionally emoted, booing when losing pitcher Steven Matz surrendered a grand slam to Marlins catcher Jorge Alfaro in the top of the sixth and cheering in the bottom of the frame when Amed Rosario countered with a grand slam of his own. As the place emptied out after the Mets gave up two more in the top of the seventh (thanks to Brad Brach’s late coverage of first base on a Harold Ramirez grounder to the right side, turning it into a two-run single), those who stayed grew more boisterous to the point where you could hear individual whistles — and individual condemnations of Callaway.

Yeah, as likeable as Mets fans seemed to find this group of players, good luck finding much love for Callaway, or his boss Brodie Van Wagenen — the pre-game presentation of awards to the Mets’ top minor leaguers of 2019 underlined the departures of Justin Dunn, Anthony Kay and Jarred Kelenic via trades — or his bosses, the Wilpons and Saul Katz.

Sure, each of those men deserves some credit for the good that has transpired. Each, however, committed his share of mistakes that led to this club falling short, with plenty of questions about its future.

Closing the credibility gap will require investment, intellect and integrity, for multiple years. It’ll take time, and for the first time in three years, the Mets did take a step in the right direction. More leaps, though, must be made in order to make this great ballpark rock in late September and beyond.