Alonso gave the Mets a 3-1 lead when he connected on a 1-1 fastball from Max Kranick (1-1) with two outs in the third inning. Alonso’s 428-foot solo drive hit a glass window on a club area just inside the left-field foul pole.
It was the 17th homer for Alonso, who is defending his All-Star Home Run Derby title on Monday night in Colorado. Alonso won the competition in 2019, and it was canceled last year because of the pandemic.
Alonso helped the Mets to the victory in front of 31,924 fans, the club’s largest home crowd since Sept. 28, 2019, when the first baseman hit his 53rd homer to break the rookie record set by Aaron Judge.
New York got off to a fast start in the second game when McNeil hit a two-run double in the first. Billy McKinney added a pinch-hit RBI single in the sixth.
It was McNeil’s first extra-base hit since he doubled against Tyler Glasnow on May 14 at Tampa Bay. Before giving the Mets a 2-0 lead, McNeil’s previous 16 hits were singles.
“I think it’s just getting comfortable at the plate,” McNeil said. “I’m starting to see the ball better and my barrel awareness is back and I’ve been able to shoot some balls all over the field.”
The Mets played their 10th of 13 doubleheaders this season. It is their most doubleheaders since playing 13 in 1979.
New York is the first team to play at least 10 doubleheaders before the All-Star break since the Toronto Blue Jays in 1978.
All-Star Bryan Reynolds hit a two-run homer in the opener and an RBI single in the nightcap for the Pirates, who were trying to sweep a doubleheader from the Mets in New York for the first time since Sept. 10, 1969. Jacob Stallings connected for Pittsburgh in the second game.
Mets right-hander Tylor Megill allowed one run and four hits in 3 2/3 innings in the nightcap. Jeurys Familia (4-1) got the final out of the fourth, and Seth Lugo allowed Stallings’ homer in the sixth.
Edwin Díaz struck out the side in the seventh for his 19th save in 20 chances. He threw just 10 pitches.
“For me this is the best outing I’ve seen him have as a Met,” New York manager Luis Rojas said.
Kranick allowed three runs and four hits in three innings. He was Pittsburgh’s 27th man for the doubleheader and was optioned to Triple-A Indianapolis after the game.
In the opener, Anderson (5-8) won consecutive starts for the second time this season, allowing two runs and six hits. He went winless in an eight-start span from May 15-June 28.
The game was tied at 2 when Anderson went deep with two out in the fifth, driving a 1-1 cutter from Stroman (6-7) over the wall in right-center. It was Anderson’s second career homer in 152 at-bats and first since July 9, 2016, for Colorado against Philadelphia.
“As soon as I hit it, I was hoping it got over the outfielder’s head,” Anderson said. “And then they were catching home runs earlier in the game. So, once it looked like it had a chance, I was hoping it wouldn’t get caught too.”
Reynolds was robbed of a home run when Mets center fielder Brandon Nimmo made a terrific leaping catch at the wall in the first. But Reynolds easily cleared the fence in right-center on his two-run homer off Trevor May in the sixth.
Stroman lost his third straight decision. He was charged with three runs and five hits in five innings.
Mets: RHP Carlos Carrasco (strained right hamstring) threw three innings and about 30 pitches in a simulated game. Rojas was particularly impressed with Carrasco’s changeup and said he could start a rehab assignment next week. ... 3B/OF J.D. Davis (sprained left hand) is continuing his rehab assignment with Triple-A Syracuse and could rejoin the team next weekend.
RHP Chase De Jong (1-3, 5.08 ERA) starts Sunday for Pittsburgh. The Mets may do a bullpen game or use an opener.