Mets fans at Citi Field showered with cheers after he hit career home run No. 300 Tuesday night, treating the franchise’s leading home-run hitter as if he’d never left New York -- even as the blast helped the Orioles send the game into extra innings.

Alonso certainly returned that level of appreciation when he received the milestone baseball from a trio of Mets fans after Baltimore’s 7-5 win. Alonso greeted the three fans outside the Orioles’ clubhouse with handshakes, hugs and effusive thanks before offering items in exchange for the ball.

All three fans were wearing Mets jerseys (two of them with Alonso’s name and number), and the Polar Bear signed them. He even personalized each signature by writing “300th HR game.”

Alonso then went into the clubhouse and returned with three brand-new bats, and before signing them, asked the group of fans if they wanted a personalized message on them.

“I can write whatever you want,” Alonso told them. “Seriously, don’t be bashful.”

After signing the lumber, Alonso dipped into the clubhouse once more, and he reappeared with beers for the fans. The Orioles slugger, who played the first seven years of his career with the Mets, then sent them off with handshakes and one more surprise.

“You guys rock,” Alonso said. “Honestly, any time you guys want to come down to [Oriole Park at Camden Yards] ... you guys want tickets, batting practice passes, whole nine yards -- on me. Thank you.” 

The fans replied appropriately.

“You are an absolute legend,” one said. “Congratulations.”