Alonso reaches 300-home-run milestone in Orioles' 7-5 extra-inning win over Mets on September 16

Pete Alonso hit his 300th career home run on September 16 against his former team, joining a historically rare club as the Orioles defeated the Mets 7-5 in extra innings at Citi Field.

Alonso's milestone came off Mets starter Kodai Senga in the top of the ninth inning with the Orioles trailing 1-0, bases empty, and one out. The home run traveled 414 feet, per CBS Sports. The 31-year-old is the 171st member of the 300-home-run club and the third player to hit his 300th home run against a team for which he played in 1,000 or more games, according to Sporting News reporting.

The homer was Alonso's 36th of the season. His slash line stands at .267/.362/.499 through 152 games played for Baltimore. He leads the American League in RBIs with 101 and carries 4.1 WAR for the season, per CBS Sports.

Alonso, who spent his entire career with the Mets through 2025 and hit 264 home runs as a Met from 2019-25, played his first game back at Citi Field as an Oriole on Monday in a 2-1 Baltimore victory, going 0 for 3 with a walk. This year, the Mets did not pursue re-signing him; he signed a five-year free agent deal with Baltimore.

Mets fans at Citi Field gave Alonso a standing ovation and chanted his name after the home run. Alonso took a curtain call in the visiting dugout. According to Sporting News, fans were also heard chanting "fire Stearns," referring to David Stearns, the team's president of baseball operations. Alonso met postgame with the Mets fans who caught the ball, exchanging it for signed baseballs, bats, autographed jerseys, offered them tickets to games in Baltimore, and brought beers.

Senga threw Alonso three straight offspeed pitches; Alonso took the first two out of the zone and launched the third one, per CBS Sports. Alonso said postgame: "There's a lot of history here with me, and honestly, it doesn't matter where and when. I just want to help the team win. No. 300, it's a nice round number. But I'm just so proud of this group. The way we fought today, it's an unbelievable team win."

Mets starter Sean Manaea criticized the crowd's reaction. "I have nothing but respect for (Alonso) and love him to death. As the 2026 Mets, we've definitely underperformed. But the guys in here work their ass off every single day, and to have that kind of reaction to an opposing player is crazy to me. I've just never seen anything like that before," Manaea said. He added: "Pete's not here. He's just not here. So I know everybody loves him. He's the man. But yeah, he's not here. So to see the reaction from the fans like that, I don't know, it's just different."

The victory improved the Orioles' record to 74-78 and kept them alive in the chase for the third and final wild card spot in the American League.