Stanton had to come out of the game after loading the bases by walking Brad Wilkerson due to a strained right knee.
The Expos scored their other three runs on a Vladimir Guerrero first inning solo homer, an RBI ground rule double by Tatis, who scored on pitcher Javier Vazquez's infield single.
The Mets showed flashes of the defensive brilliance that helped them lead the league in errors last year, with Rey Sanchez's bobble of Vladimir Guerrero's ground ball helping to set up the eighth inning rally that won the game for the Expos. Timo Perez overthrew Rey Sanchez while throwing the ball back in after a single, and second basemen Roberto Alomar let the ball roll past him, allowing Orlando Cabrera to take second. Cabrera would eventually score on Tatis' ground rule double.
In addition, Mike Piazza allowed three stolen bases, overthrowing second base on one of his throws. This loss overshadows another solid performance from starting pitcher Steve Trachsel, who pitched six strong innings, allowing only 3 runs.
The Mets, now 4-9 and five games out of first place, head to Pittsburgh where they take on the surprising Pirates tomorrow on the last leg of their road trip. Tom Glavine will be on the hill tomorrow to take on Josh Fogg.