Pinch hitter Terry Crowley singled in Argenis Salazar from third with none out for the go-ahead run in a three-run eighth that gave Montreal a sweep of its doubleheader with visiting St. Louis.
In the opener, Bryn Smith pitched a five-hitter and Bryan Little and Doug Flynn each drove in a run.
The defending world champion Cardinals dropped their sixth straight and are seven games out of first.
Crowley, a veteran pinch hitter, said he came to the park early. "I got together with (batting coach) Billy DeMars and did some hitting off the tee," he said. "I wanted Billy to see if he could get me back to the way I was swinging when I broke into the minor leagues."
Hitting off the tee was good preparation for facing reliever Bruce Sutter's split-fingered fast ball.
"The last thing you want to do is pull off the ball on a split-fingered fast ball," said Crowley. "I was determined to keep my front shoulder in."
Tim Wallach opened the eighth with a double off reliever Dave Rucker (5-3) and Salazar ran for him. Sutter relieved and pinch hitter Terry Francona reached on a fielder's choice with Salazar going to third. Crowley then singled to right.
After Chris Speier beat out a bunt, Tim Raines singled in a run. One out later, Andrew Dawson hit a sacrifice fly for his 110th RBI, breaking a team record set last year by Al Oliver.
In the opener, the first two Expos to face Cardinals right-hander Neil Allen (11-13) produced a run as Raines doubled and Little singled.