Expos starter Tony Armas, Jr was keeping the Mets in check until the fifth inning, when Roger Cedeno singled in Rey Ordonez to tie the game.
Piazza's first home run of the night gave them the 2-1 lead.
It all fell apart for the Mets in the bottom of the sixth. Mike Bacsik, who had been pitching well after a shaky first inning, walked Vladimir Guerrero to lead off the inning. Cabrera hit a ground ball to advance Guerrero to second. Then it got screwy. Rookie Matt Cepicky hit a grounder to Ordonez. Ordonez saw Guerrero break for third and threw to third to try to get him, but wound up hitting him in the back and Guerrero was safe at third. Since the ball hit the backstop, the Mets were lucky he didn't score. Perhaps trying to stave off a bad inning, Bobby Valentine immediately yanked Bacsik, and brought in the submarining Steve Reed. That didn't work, as Michael Barrett doubled off of Reed to score both Guerrero and Cepicky. Troy O'Leary then walked, and Reed gave up a double to score both Barrett and O'Leary. 5-2 Expos.
Piazza's second home run of the game made it 5-3 in the eighth.
Ty Wigginton hit an opposite-field home run in the ninth to draw the Mets within one, but that was all they could do.
Notes-The Mets made two more errors, making a total of eight in the past two games.
-Piazza's two home runs gave him a total of 30 for the season, giving him nine seasons where he has hit at least 30 home runs.
-The Mets will try to salvage at least a split of this four-game series. Pedro Astacio (12-9, 4.29), who has struggled his last five starts, will pitch for the Mets, while Javier Vazquez (9-13, 4.06) will pitch for the Expos.