Pete Alonso has been entangled in the offensive stagnation plaguing the Mets, with the first baseman entering Friday’s series opener against the Giants on an 0-for-17 slump.

But Alonso sparked the Mets lineup in the seventh inning of a 4-3, 10-inning loss at Citi Field.

After striking out in each of his first two at-bats of the night against left-hander Robbie Ray, Alonso led off the bottom of the seventh.

With the Mets trailing by three runs and having not scored since Tuesday, Alonso proceeded to belt his 23rd homer of the season.

It cut the Mets’ deficit to two runs and the shot to right-center was only the Mets’ third hit of the night versus Ray.

The homer was also just Alonso’s second homer in his past 18 games.

It left Alonso three home runs away from Darryl Strawberry’s franchise record 252.

Alonso followed it up an inning later with a game-tying sacrifice fly.

Following Ray’s departure after seven innings, the Mets got to San Francisco’s bullpen.

Brandon Nimmo drew a walk, and Francisco Lindor followed with a single, setting the stage for Juan Soto’s RBI hit that landed in short left field, making it 3-2 while putting runners on the corners.

Alonso’s fly ball to center scored Lindor to tie the game at 3-3.

But after Ronny Mauricio’s pinch-hit walk, Brett Baty — hitting for Mark Vientos — grounded out to keep the game tied.

Alonso also walked.

“There were some good signs from Pete today,” Carlos Mendoza said.

“When I get out of my plan, I chase off-speed [pitches],’’ Alonso said. “I chased some heaters tonight, but laid off the breaking stuff.”

The Mets are hopeful that Alonso’s 414-foot, 110-mph home run — along with a 108-mph sac fly off former teammate José Buttó — signals the start of a turnaround. Before the game, he was just 5-for-60 with 19 strikeouts, contributing to the struggles in the heart of the lineup.

Lindor entered just 9-for-63 with 19 strikeouts in his previous 14 games, while Soto was in a 4-for-37 rut before his RBI hit in the eighth.

Alonso, of course, helped carry the Mets offense for much of the first month of the season while Soto got his footing in Queens.

Only the Phillies’ Kyle Schwarber has driven in more runs in the National League this season than Alonso, who is looking to get the Mets going down the stretch.

“This is what you play for,’’ Alonso said. “This is what it’s all about.”