For eight innings, this one looked like another ugly, lifeless Mets defeat.

They didn’t get a hit until the sixth and had just a pair of hits heading into the ninth against Miami closer Tanner Scott.

But in the ninth, a leadoff walk by Francisco Lindor was followed by a one-out, game-winning, two-run homer from J.D. Martinez.

It gave the Mets a dramatic 3-2 win over the last-place Marlins, as they avoided a series defeat at Citi Field

For Martinez, it was the first walk-off home run of his lengthy career, and for the Mets, it was their sixth win in eight games.

“I’d never done it before, so I didn’t know how to act when I hit it,” Martinez said. “It was definitely cool.”

“We needed that,” Carlos Mendoza said. “It was a good one. Every time we win a game — especially that way — it’s important. So is winning series.”

They also got a scoreless ninth from Edwin Diaz, who threw well in his return from the injured list with a right shoulder impingement.

Early on, this had the makings of another dreary night in Queens.

No-hit by right-hander Roddery Munoz for 5 ¹/₃ innings, the Mets got a run in the seventh but still trailed by a run with three outs remaining.

After Lindor’s walk, Brandon Nimmo struck out.

With Martinez at the plate, Lindor swiped second and on the next pitch, Martinez went deep for his sixth homer of the season.

The win salvaged a solid outing from Luis Severino, who could be in the conversation for an All-Star berth — and a trip out of Queens at the trade deadline.

Severino pitched at least six innings and gave up just one run for the third time in his past four starts as he builds his case for an All-Star nod after last year’s disaster with the Yankees.

But after scoring 10 runs in Wednesday’s win, the Mets didn’t get a hit off Munoz until Harrison Bader’s single to right with one out in the sixth.

Munoz, a 24-year-old rookie, had allowed 10 earned runs over 8 ²/₃ innings in his previous two starts for the Marlins — with a stint in the minors in between.

Severino, coming off another excellent start against the Nationals, was far from dominant.

Still, he pitched out of trouble in the third, fourth and fifth innings, allowing multiple base runners in each frame, but escaping unscathed.

Miami finally broke through against Severino in the sixth.

With one out, Jake Burger smacked an opposite-field solo homer to right on a 1-2 four-seam fastball. It gave the Marlins a 1-0 lead and was just the second home run allowed by Severino in his past four starts.

Bader then got the Mets’ first hit, but was caught stealing with Lindor at the plate.

Drew Smith replaced Severino to start the seventh and gave up a one-out bomb to Jazz Chisolm Jr., a 426-foot solo homer, to make it 2-0.

Lopez, despite allowing just three base runners and facing one batter over the minimum, was pulled after 81 pitches, with Anthony Bender coming in.

Nimmo, in a nearly month-long rut, led off with a walk and Martinez sent him to third with a double down the left-field line.

A walk by Pete Alonso loaded the bases for Starling Marte.

Marte grounded into a double play to score Nimmo for the Mets’ first run, but Mark Vientos followed by bouncing out to shortstop to end the threat.

Diaz pitched a scoreless ninth to set up Martinez’s heroics, as he delivered a 409-foot shot to right-center.

“We’ve been grinding all year,’’ Martinez said. “To get Diaz back is huge. Hopefully we can get on a roll here.”