PITTSBURGH — The Mets were in the familiar position of disappointment Sunday following a blown lead by the bullpen, but they at least had a chance to rectify the matter.

Methodically, they built a rally in the ninth inning and received the big hit they needed from Francisco Lindor, whose two-out, two-run single put the Mets ahead for good in a 3-2 victory over the Pirates at PNC Park.

Lindor’s single buried former Yankees closer Aroldis Chapman, a half-inning after Edwin Diaz flushed a one-run lead.

Francisco Alvarez began the go-ahead rally in the ninth with a leadoff walk and Harrison Bader singled.

Chapman struck out Mark Vientos and pinch-hitter Luis Torrens before Jose Iglesias walked to load the bases.

Lindor — who learned after the game he was left off the NL All-Star team — reached base four times Sunday.

Sean Manaea, who bolstered the Mets with six shutout innings, watched the late-inning drama unfold on TV in the clubhouse.

“It’s a beautiful thing about baseball, you can be on the edge of your seat the whole time, you can be down in the dumps but it can bring you back up,” Manaea said. “There was a lot going on, but this is what makes this game.”

After allowing two singles surrounding an out on a fouled bunt for strike three to open the eighth, Dedniel Nunez struck out Bryan Reynolds for the second out, prompting manager Carlos Mendoza to signal for Diaz, one day after the closer had returned from a 10-game suspension for violating MLB’s rules on foreign substances.

On Saturday, Diaz had a largely uneventful ninth with a three-run lead and received the save, but on this day walked Joshua Palacios to load the bases before Nick Gonzales delivered a single through the shortstop hole for a two-run single that gave the Pirates a 2-1 lead.

Diaz returned to the mound after Lindor’s go-ahead single and worked a perfect ninth.

“Those guys battled in the ninth inning, so I told myself, ‘We have got to get the [win] any way,’ ” Diaz said. “That’s what I did, make pitches and get weak contact.”

Lindor saw a 101-mph heater for a ball from Chapman on the first pitch of his at-bat in the ninth and then took a slider for strike.

Lindor hit a slider to left field to bring in the tying and go-ahead runs.

“It just felt like everybody was seeing every single pitch and cheering,” Lindor said of the ninth-inning vibe. “And talking about the approach and making sure we were at least going to tie the game against him.”

Brandon Nimmo’s RBI double in the eighth against former Mets reliever Colin Holderman broke the scoreless deadlock.

Lindor reached base for the third time in the game, drawing a two-out walk, before Nimmo delivered with a shot to left-center.

Manaea gave the Mets six scoreless innings in which he allowed two hits and walked three with six strikeouts.

It was a second straight appearance for the left-hander of pitching at least six innings after going seven straight starts without reaching that mark.

The Mets were glad to see Luis Ortiz depart after the six innings.

The fireballing right-hander, in his second start of the season, allowed only four hits without walking a batter over six shutout innings.

Ortiz provided two scoring chances for the Mets: Lindor’s two-out single in the third got Vientos to third base before Nimmo struck out in a second straight at-bat.

Lindor doubled in the sixth and reached third on Nimmo’s ground out, but J.D. Martinez was retired to end the threat.

The Pirates put runners on base throughout against Manaea, but the lefty succeeded in avoiding damage.

In the first he walked two batters, but got Reynolds to hit into a double play that helped suffocate the inning.

In the second Manaea missed the bag covering first base, allowing Ke’Bryan Hayes to reach leading off the inning, but followed with three straight outs.

Hayes in the inning got as far as third base, with a wild pitch and stolen base.

In the fifth Joey Bart hit a shot past third base, but was thrown out by left fielder Jeff McNeil trying to stretch it into a double.

Manager Carlos Mendoza said once Diaz got warmed up in the eighth he was determined to use the closer for a four-out save.

After Diaz entered and watched two inherited runners score he was told to be ready for the ninth.

“He’s our closer, he’s our guy and for us to get where we want to get we are going to need him,” Mendoza said. “Today a weak ground ball got through, but then he got the job done in the ninth.”