Vokoun was pulled after Boston grabbed a 3-0 lead late in the opening period of a 6-1 win in Game 2. He was replaced by Marc-Andre Fleury.
The Bruins struck quickly again Wednesday when David Krejci scored just 1:42 in on Boston's first shot of the game.
Vokoun originally earned the starting job after Fleury struggled in the Penguins' opening-round series against the New York Islanders.
Penguins coach Dan Bylsma said after the team's morning skate Wednesday that Vokoun has been steady nearly every game he has played this post-season.
Boston leads the series 2-0 and hosts the next two games.