NEW YORK -- Frustration bubbled up in the aftermath of the Mets’ 7-5, 11-inning loss to the Orioles on Tuesday, as various Mets expressed disappointment in fans who spent the night cheering against their own players.

The issue was most acute after Pete Alonso hit his 300th career homer in the ninth inning. Fans, who packed into Citi Field for two consecutive nights to welcome Alonso back to his former home, gave him a loud ovation while chanting his name. They rose to their feet again in anticipation when Alonso came to bat in the top of the 11th with a chance to win the game.

“I’ve just never seen anything like that before,” starting pitcher Sean Manaea said. “The guys in here, we are grinding our butts off and stuff like that happens. But I’ve never seen anything like that. It’s kind of crazy.”

Kodai Senga, who gave up Alonso’s 300th homer, said he might have been offended under ordinary circumstances, but because he understood how beloved Alonso is in Flushing, he did not feel that way on this occasion.

Still, the circumstances were extraordinary, with fans eliciting a curtain call from Alonso after No. 300.

“I appreciate all the support, especially for all the years I’m here, all the life I’ve lived here,” Alonso said. “Obviously they’re recognizing that and they appreciate that. It’s a two-way street. I really appreciate it.”

The Mets also flashed a brief congratulatory message on their scoreboard after Alonso hit No. 300.

“People are free to do whatever they want to do on the field,” interim manager Andy Green said. “Our job is to never let anything external impact the way we go about playing the game. I think that’s tough in certain circumstances. I think guys may struggle with that at times.

“Do we love our fans cheering for us? Heck yeah we do. Do we want our fans engaged with us? Heck yeah we do. We absolutely want that. And those guys on the field are giving everything they’ve got for the team, for the Mets across their jerseys. Those guys will continue to do that day in and day out. We understand -- we’ve made abundantly clear we understand -- we didn’t meet expectations this season. We’re going to show up tomorrow to win a baseball game.”

The Mets drew crowds of 35,800 and 28,097 for the first two games of this series, with many fans sporting Alonso jerseys.

After Monday’s opener, shortstop Francisco Lindor expressed disappointment that Mets fans offered relatively little support for their own starting pitcher, Jonah Tong. At one point midway through the game, fans booed Tong when he walked Alonso.

“I think next time, they’ve got to give the pitcher a little more love, too,” Lindor said.

“It’s crazy,” Manaea added a night later. “Pete’s not here. … He’s just not here. I know everyone loves him. He’s the man. But he’s not here. So to see the reaction from the fans like that, I don’t know. It was just different. I’ve never seen anything like that.”