NEW YORK -- Chad Green was one of the Yankees’ most dominant relievers through the first three weeks of the regular season, allowing one run across nine appearances. That has turned, as the right-hander is suddenly struggling with the long ball.

Green served up three home runs, including Pete Alonso’s game-tying three-run shot and Dominic Smith’s go-ahead blast, as the Mets rallied to extend the Yankees’ losing streak to a season-high six games with a 6-4 loss in the first game of Friday’s doubleheader at Yankee Stadium.

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“We get to go right after it again, so that's the good part,” said manager Aaron Boone. “We’ve just got to find a way. The last couple of games, we’ve had some great starting outings and haven't been able to finish off the win. We get to try again tonight.”

As the clubs prepared to play five Subway Series games in three days, it marked the second successive ineffective outing for Green, who surrendered a go-ahead homer to the Braves’ Freddie Freeman on Wednesday at Atlanta.

This time, Green’s stumble spoiled a solid effort from left-hander Jordan Montgomery, who used his fastball and changeup aggressively to blank the Mets over the first four frames.

Smith scored on a fifth-inning wild pitch and Montgomery allowed hits to the first two batters in the sixth, prompting a move to the bullpen with Montgomery at 68 pitches.

“It's been 12 days since I've been in a game and I threw [49] pitches five days ago [because of rain], so I'm not really built up right now,” said Montgomery, who struck out six and did not walk a batter.

Jake Marisnick extended the Mets’ lead by going back-to-back with Smith off Green, who has seen his ERA jump from 0.71 to 3.68 in two appearances.

“I like Green in just about any situation,” Boone said. “He’s had a couple of bumps here, but once we’re there, I had a lot of confidence in him at that point. It wasn’t a great day today, but I felt like he got a couple of pitches where he wanted. They just put better swings on him.”

Luke Voit and Clint Frazier continued to swing hot bats atop the Bombers’ lineup. Voit stroked three hits and scored twice, while Frazier homered as part of a three-RBI performance.

Frazier doubled home the game’s first run in the first, then clubbed a two-run shot in the second off Mets starter Michael Wacha, who lasted three innings.

Estevan Florial, the Yanks’ No. 7 prospect according to MLB Pipeline, picked up his first Major League hit with a fifth-inning single off right-hander Walker Lockett.

The Yanks were unable to push more across facing Lockett, who worked two scoreless frames to earn the victory, then was designated for assignment after the game.

Dellin Betances worked a scoreless sixth inning in his first appearance against his former team, pitching around a hit batsman and a walk. Edwin Díaz struck out the side in the seventh inning to secure the save.

“No one likes losing, so we're definitely doing our best to break this rhythm of losing and find our way again,” Montgomery said. “We're playing hard and some things aren't going our way, but I guess that's baseball. We'll just keep grounded and do our best to break it.”