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PITTSBURGH — Carlos Mendoza rearranged the deck chairs Saturday, but the Titanic still sank.

Mark Vientos got placed into the lineup’s No. 2 hole — which has mostly been Brandon Nimmo or Starling Marte’s domain lately — with the idea it might jump-start the third baseman, who just returned from the injured list a day earlier, against a left-handed starting pitcher.

Then it rained in the top of the second inning, and after a delay of 1 hour, 29 minutes, the Pirates changed pitchers. Mendoza stood pat with Paul Blackburn.

In the end the Mets were left soggy. Blackburn got stomped right out of the delay and the lineup continued its pattern of disappointment in a 9-2 loss to the lowly Pirates at PNC Park, which later led to a players only team meeting.

Mendoza wasn’t around to watch much of it from the dugout.

He was ejected in the fourth inning for arguing balls and strikes.

The manager’s biggest decision was letting Blackburn return for the second inning following the rain delay.

The Pirates got five straight singles against the right-hander and scored three runs, leaving the Mets to play catch-up.

Mendoza said he thought Blackburn could give the Mets another 35-40 pitches following the rain delay.

“Obviously not an easy [decision], but given where we are bullpen wise, especially in this stretch of the last 12 days where we haven’t gotten length from our starter, we kept [Blackburn] throwing at high intensity,” Mendoza said, referring to the rain delay. “We knew it wasn’t one of those where he was going to go back out and we were going to try to get him through five [innings]. It was just more that if we could get an extra 35-40 [pitches], we could use it.”

Wasted was a mostly strong performance from the Mets bullpen, which pitched six scoreless innings before Huascar Brazobán surrendered four runs in the eighth.

Colin Poche allowed another two in a mop-up role.

Now the Mets will have to figure out how to navigate Sunday’s series finale — at least one reinforcement will likely be needed from Triple-A Syracuse — with a bullpen further on fumes.

Blackburn, in a third straight subpar start, allowed three earned runs over one inning on six hits with two strikeouts.

The right-hander, who has been thrust into the rotation because of injuries, saw his ERA jump to 7.71.

“I was just hoping that I could cover a couple of innings coming off that rain delay,” Blackburn said.

The Pirates jumped on Blackburn immediately following the rain delay. Oneil Cruz, Joey Bart, Spencer Horwitz, Ke’Bryan Hayes and Isiah Kiner-Falefa singled successively to begin the inning, placing the Mets in a 2-1 hole.

José Buttó was summoned from the bullpen and Adam Frazier’s sacrifice fly added a run. Buttó struck out Bryan Reynolds with the bases loaded — following a catcher’s interference by Luis Torrens with Andrew McCutchen at the plate — to keep the game in check.

Mendoza was ejected in the bottom of the fourth after complaining to plate umpire Roberto Ortiz about his strike zone. The ejection was Mendoza’s first this season and the third of his career.

Nimmo’s RBI single in the fifth pulled the Mets to within 3-2.

Pete Alonso delivered a one-out double before Nimmo delivered. But any chance of a further rally was quashed with strikeouts by Marte and Tyrone Taylor.

Marte walked leading off the eighth but was erased when Taylor hit into a double play. The Mets were 2-for-8 with runners in scoring position and left 10 runners on base.

Vientos went 1-for-5, with an infield hit in the ninth. While the Mets received sporadic production from the bottom of the order (an improvement), a scoring outburst never arrived.