Pete Alonso of the Mets rounds third base after hitting a two-run...

Pete Alonso of the Mets rounds third base after hitting a two-run home run in the third inning of a game against the Red Sox at Fenway Park on Monday in Boston. Credit: Getty Images/Adam Glanzman

BOSTON — After Pete Alonso couldn’t get into the Green Monster, he tried to knock it down.

Minutes before first pitch of the Mets’ 7-4 win over the Red Sox on Monday night, their slugging first baseman — 1-for-11 with five strikeouts in the opening weekend — jogged over to Fenway Park’s famous leftfield wall, bent over and peered through a small opening.

A self-described history nerd, Alonso wanted to do what so many before him have done: slap his signature on the inside of the Monster. But because of MLB’s health protocols during this pandemic-threatened season, he wasn’t allowed. The manually operated scoreboard was only half-operational. His disappointment was immense. “I’m not a little upset,” he said. “I’m a lot upset.”

He was slightly less upset by the top of the third, when his rocket of a line drive ricocheted loudly off a row of fan cardboard cutouts and back onto the field.

The Mets (2-2) scored all of their runs on homers by Michael Conforto, Alonso and Dominic Smith. Conforto’s long ball came first (second inning, breaking a scoreless tie) and Smith’s counted for the most runs (three, in the fourth inning). But neither was a more violent feat of round bat striking round ball than Alonso’s shot.

Alonso got a 3-and-0 changeup over the middle of the plate from lefthander Jeffrey Springs and pulled it at 116.3 mph over the 37-foot-high wall. It was his first homer of the year and the 54th of his career.

“It’s been a little while since I hit my last homer,” said Alonso, who snapped a four-game, 10-month homerless drought. “So it’s nice to get that one out of the way.”

A home-run ball hit by the Mets' Pete Alonso bounces...

A home-run ball hit by the Mets' Pete Alonso bounces between fan photographs placed in the seating section on top of the Green Monster seating section during the third inning of a game against the Red Sox on Monday at Fenway Park in Boston. Credit: AP/Charles Krupa

Said Smith, “That was an absolute bullet. I’m glad there weren’t any fans up there, because somebody could have gotten hurt with that one.”

Michael Wacha allowed one run in five innings in his debut with his new team, with a solo shot by Mitch Moreland the only blemish. The Mets’ pitching the rest of the night wasn’t as smooth, though.

Although the Mets led by seven runs as late as the sixth and five runs in the eighth, Luis Rojas wound up calling on Seth Lugo to record the final four outs — which he did, retiring all four batters he faced.

Jeurys Familia allowed two runs in two-thirds of an inning, turning what had been a blowout into a save situation.

Conforto got the scoring started when he walloped a 434-foot shot off lefthander Josh Osich, the first of five Red Sox pitchers.

Reliever Paul Sewald — leaving the bullpen overflow seating in the actual stands — retrieved the ball and pretended he was going to throw it back onto the field. He did not.

Smith, slotted in as the designated hitter in his first start of the season, turned it into a blowout — temporarily — with a line-drive homer to right-center.

The Mets’ seven runs were more than they totaled in their first three games (five).

“We know how talented this lineup is,” Smith said. “We’re used to saying it’s a long season. Obviously, it’s not. It’s a shorter season. So we know we have to get it going . . . To see a little breakthrough like this is definitely a good sign.”

They’ll try to do that again Tuesday to finish the Boston half of this four-game home-and-home series. Right after Alonso takes another shot at leaving his mark on — or in — the  Green Monster.

“I was really upset that this year we’re not able to do it,” he said. “Or hopefully I can finagle my way in there tomorrow.”

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