Jim Wohlford's pinch-hit single with two out in the eighth inning scored Vance Law with the winning run as Montreal, at home, defeated Pittsburgh.
Wohlford lined a 1-0 pitch from John Candelaria to score Law, who had tripled off starter Jose DeLeon (2-9) earlier in the inning.
"I went up there swinging," said Wohlford. "I like pinch-hitting, especially when the game is on the line. If they stay with me, I know I'm going to do the job. I realize I've been pressing lately, but I still have four game-winnners. That's not bad for a part-time player."
Tim Burke (3-0) pitched 3 1/3 innings of one-hit relief. Jeff Reardon pitched the ninth inning to earn his major league-leading 20th save.
Hubie Brooks gave the Expos a first-inning lead with a two-out, three-run homer after Tim Raines and Law had started the inning with walks.
Pittsburgh tied the score with a three-run third off starter Joe Hesketh. DeLeon struck out to start the inning but reached first on Mike Fitzgerald's passed ball. Bill Almon hit the next pitch for his fourth home run of the year.
Jim Morrison beat out an infield single and, one out later, George Hendrick doubled him to third. Tony Pena's grounded out to scored Morrison.