NEW YORK -- What the Mets feared in shifting Seth Lugo to the rotation this week was exactly what unfolded in the eighth inning Wednesday at Citi Field. Riding high after seven brilliant innings from Jacob deGrom, the Mets carried a three-run lead into the eighth. Then they watched that lead, like so many others deGrom has compiled over the years, evaporate.

That the Mets were able to escape with a 5-4 win over the Marlins was a credit to Wilson Ramos, who plated Billy Hamilton with a go-ahead RBI single in the eighth, and Brad Brach, who recorded the final four outs. But the whole situation underscored an end-game problem the Mets have yet to solve. Despite employing a much-improved bullpen over the past few weeks, the Mets still don’t know on a nightly basis who will close out games for them.

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“We trust our guys,” Mets manager Luis Rojas said. “We know their ability to get outs, to get strikeouts, throw in stress situations, tension situations. It’s something they’ve done in the past and they’re going to be able to do.”

For most of Wednesday evening, it did not appear Citi Field would play host to a close game. The Mets jumped in front of Marlins starter Elieser Hernandez on a Robinson Canó RBI double and solo homers by Michael Conforto and Brandon Nimmo. Considering the extent to which deGrom was cruising -- he matched his career high with 14 strikeouts, retiring seven of the final nine batters he faced in that fashion -- the Mets seemed ready to cruise to victory.

But as soon as deGrom departed, things grew hairy. Justin Wilson allowed hits to three of the four batters he faced in the eighth, prompting the Mets to turn to Edwin Díaz -- once again the de facto closer now that Lugo is in the rotation. He allowed an RBI infield single and walked in a run, before left leg cramps forced him to depart.

“He wanted to keep going,” Rojas said. “He wanted to stay in there. … Thank God it’s not a major issue. It’s nothing of major concern right now.”

Entering with a 2-1 count against Brian Anderson, Brach walked in another run to tie the game and stick deGrom with a no-decision. But Canó led off the bottom of the eighth with a single, and Hamilton -- pinch-running for Canó -- raced around with the go-ahead run on Ramos’ hit. Brach then recorded the final three outs to pick up the win that once belonged to deGrom.

That has been a theme for deGrom, who has endured 14 outings over the last three seasons in which he has gone at least seven innings with one or zero runs, and not won the game. No other Major League pitcher has had more than seven such games over the same stretch, due in large part to the ineffectiveness of New York’s bullpen behind deGrom.

For years, Lugo had been such a stabilizing force to that group that the Mets resisted making him a starter, until finally caving earlier this month. And if Lugo’s three strong innings in his first start on Tuesday were any indication, it was a move that the Mets will not regret making.

Still, Lugo’s absence from the bullpen leaves a hole that the Mets must figure out how to fill. One option, Díaz, has struggled for most of the last two seasons. Another, Dellin Betances, owns a 6.00 ERA and wasn’t called upon in either the eighth or ninth inning Wednesday despite not pitching for a full week. Wilson and Jeurys Familia have had their hiccups.

For the Mets’ bullpen to succeed without Lugo, more than one of them will need to thrive in the future.

“We definitely liked him in the bullpen to be the multi-inning guy, to close games when we needed him to,” Rojas said of Lugo. “But right now, that’s just not the case. He’s in our rotation, and we like our guys. And we feel that we have so much depth, and we have guys that can definitely help us close games.”