Alonso added a second homerun in the ninth, making him the Mets’ first player with a multi-homer game this season.
Valaika tied the game at 2-2 with a two-run double in the second, then scored on a Mullins brace. Valaika doubled another point in the third.
Mullins started off with a brace in the fourth quarter – by then he had made 11 hits in his last 13 batting – and scored on a Trey Mancini single.
Mets manager Luis Rojas said the plan was still for a struggling Peterson to make his next scheduled departure.
“We have to fix it,” Rojas said. “We need David Peterson.”
Franco opened the game with a three-run homerun in the fifth that crossed the line into left field and into second bridge. He was the first player to hit a home run at this level since Alonso last September. Mark Reynolds in 2011 and Manny Machado in 2017 were the only Baltimore hitters to do so before.
Santander hit a solo homer in the eighth.