The series that wouldn’t start has become the series that won’t end.

A three-game set that has meant virtually nothing for the Mets and virtually everything for the Marlins could require one, final day of baseball after one long, unfinished night of baseball.

Thursday’s series finale was suspended with the Marlins up, 2-1, and four outs to go because weather intruded and would not leave.

The Marlins might have to return to Citi Field on Monday — a day after the season is supposed to end — to play less than an inning, if the playoff race is still undecided after Sunday.

The Mets were two outs from securing the game and the series, but a ninth-inning blown save allowed the Marlins to take the lead — and allowed more time for Mother Nature to move in.

The game entered a delay at 9:41 p.m. in a driving rain, and the Mets announced the game was officially suspended in the same driving rain at 12:58 a.m. Friday.

The league, which does not want to interrupt the one day clear of games in between the regular season and playoffs, clearly did not want play suspended.

“Kept looking for a window,” Mets manager Buck Showalter said after the 3-hour, 17-minute delay.

At about 12:22 a.m., when the rain had slightly eased up, the grounds crew removed the tarp from the infield and brought it to deep left field.

But shallow left field and much of the outfield and foul territory appeared swampy.

Marlins brass, including general manager Kim Ng and manager Skip Schumaker, briefly met with Brandon Nimmo — apparently the Mets representative — on the field at about 12:25 a.m.

Reps from both teams and MLB continued to talk for the next 10 minutes, and Mets players returned to the dugout — before the tarp was dragged back on the field.

At about 12:43 a.m., Pete Alonso met with Josh Bell and Jazz Chisholm Jr. in the middle of a large puddle near the Marlins’ dugout. Conversations continued, but so did the rain.

“Long,” Mets starting pitcher David Peterson said about the delay. “Pretty boring. Ready to go home.”

Before play was stopped, there were two outs in the top of the ninth while the Marlins led, 2-1, with runners on first and second base.

By MLB rules, a regulation game that is terminated early in the middle of an inning in which the visiting team has taken the lead becomes “a suspended game that will be completed at a later date from the point of termination.”

The question now becomes whether the Marlins need to make up the game to decide a wild-card spot. Miami will open a three-game series in Pittsburgh on Friday.

After the Cubs lost Thursday, the Marlins (82-76) are half a game up for the final spot.

The Mets (72-86) are supposed to finish up a lost season this weekend at home against the Phillies.

This Mets-Marlins series began with Miami upset that Tuesday’s game could not be played because of poor field conditions — the infield dirt a mess several hours after rain had stopped — which spoiled the Marlins’ final-week rotation plans.

The pitching-needy Marlins were forced to play a doubleheader Wednesday (which was split) before enduring a nearly six-hour marathon Thursday.

The rain delay, suspension and wacky Monday what-if would have been avoided if the Mets’ bullpen did its job. The Mets entered the top of the ninth up, 1-0, but Grant Hartwig and Anthony Kay combined to allow two singles and a double that scored two Marlins runs.

Instead of the Mets celebrating playing spoiler, they dug a hole and then sat around in their clubhouse awaiting a game that rain would not allow to continue.

Until the Mets’ bullpen and the weather wreaked havoc, the Marlins could do little against Peterson, who threw seven shutout innings. His only run of support came in the eighth, when Rafael Ortega singled in Brett Baty.

The Mets have seemingly waited all year for this disappointing season to end. They might have to wait a day longer than expected.

“It’s fine,” Showalter said. “It’s what we do for a living. We play games. If that means we play another game, we’ll play.”