Trailing 6-0, the Pirates scored all their runs in the final two innings – five in the eighth and four in the ninth.
J.D. Davis hit a pair of two-run homers for New York in his first start since coming off the 60-day injured list, and rookie starter Tylor Megill pitched six scoreless innings.
But it wasn’t enough on a miserable day for the Mets, who detailed injuries to star shortstop Francisco Lindor and ace Jacob deGrom before the game.
Lindor is out indefinitely with a strained oblique, and deGrom is sidelined with forearm tightness in the latest round of health setbacks for the NL East leaders.
New York dropped to 2-4 against the last-place Pirates over the past 10 days — including two blown saves by Díaz in games the Mets led by at least five runs.
This time, he was tagged with his third blown save in 21 chances this season after Seth Lugo gave up five runs in the eighth inning.
Down 7-5 in the ninth, the Pirates loaded the bases with one out as Ke’Bryan Hayes was hit by a pitch, Bryan Reynolds walked and John Nogowski hit an infield single.
Díaz (3-4) appeared on his way to escaping the jam when he struck out Gregory Polanco looking on a full-count pitch. But then Stallings pulled his slam down the left field line beyond the outstretched glove of Kevin Pillar, who climbed over the wall in a desperate attempt to make the catch.
Díaz had not allowed a home run in 48 1/3 innings dating to last season, the longest active streak in the majors.
Stallings got his sixth career game-ending RBI. It was the third walk-off slam at PNC Park, which opened in 2001.
Nogowski, who got into a heated exchange with Mets pitcher Marcus Stroman the previous night, had three hits and is batting .514 (19 for 37) in nine games since being acquired from St Louis for cash. Stallings and Hayes had two hits each.
Clay Holmes (1-1) got the win despite giving up a solo home run to Brandon Nimmo in the top of the ninth that increased New York’s lead to 7-5.
Davis finished with three hits. Michael Conforto had two doubles for the Mets, and Nimmo drew three walks.
Megill, seeking his first major league win, left with a 6-0 lead after scattering six hits. He had two strikeouts and no walks while throwing 93 pitches.
But the Pirates scored five times off Lugo in the eighth. Pinch-hitter Wilmer Difo capped the outburst with a three-run homer that made it 6-5.
Pittsburgh rookie Trevor Crowe allowed both of Davis’ homers as the Mets got four runs and six hits off him in 5 1/3 innings.
New York extended its lead to 6-0 in the seventh when rookie Travis Blankenhorn doubled home a run as a pinch-hitter and scored on Jeff McNeil’s single.
Nogowski started the Pirates’ comeback with an RBI double in the eighth.
HOME ON THE ROAD
Attendance was announced at 27,222, largest of the season at PNC Park. The crowd had a distinctively New York flavor, though.
The visitors were cheered loudly throughout the game and nearly the entire upper section of the left field bleachers was populated by Mets fans. There was also a large pocket of Mets supporters sitting behind the New York dugout.
REMEMBERING THE CHAMPS
Eleven players from the Pirates’ 1971 World Series championship club were honored during a pregame ceremony. Hall of Famer Roberto Clemente led Pittsburgh to victory over the Baltimore Orioles in seven games in the Fall Classic that year, the fourth of five World Series titles for the franchise.
Mets: Lindor was placed on the 10-day injured list before the game and will be evaluated on a week-to-week basis after getting injured Friday night. Blankenhorn was recalled from Triple-A Syracuse, and Luis Guillorme started at shortstop. … DeGrom is day-to-day after feeling discomfort Friday while throwing a bullpen. An MRI showed no structural damage.
Pirates: Polanco (bilateral adductor strain) was activated from the 10-day IL and went 1 for 4. He had been out since July 6. INF Rodolfo Castro was optioned to Double-A Altoona. … LHP Steven Brault (left lat strain) made a rehab start for Triple-A Indianapolis and allowed one run in three innings with two strikeouts while throwing 28 of 37 pitches for strikes. He has been sidelined all season.
Mets RHP Taijuan Walker (7-3, 2.50 ERA) will oppose RHP JT Brubaker (4-9, 4.47) in the series finale Sunday. Walker pitched an inning Tuesday in the All-Star Game and allowed a home run to Tampa Bay catcher Mike Zunino. Brubaker has lost his last five decisions.
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