Vokoun was given his chance after the New York Islanders beat the Penguins 6-4 in Game Four of the first round.
The Czech netminder has repaid the faith shown in him by coach Dan Bylsma, winning two in a row to eliminate the Islanders and making 35 saves on Tuesday to repel the Senators.
Pascal Dupuis scored his NHL-leading sixth goal of the playoffs while Paul Martin, Evgeni Malkin and Chris Kunitz also tallied for the top seeded Penguins.
Colin Greening netted the lone goal for Ottawa, who had brushed aside Montreal in five games in the first round.
Game Two of the Eastern Conference semi-final is on Friday, again in Pittsburgh.
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- Ice Hockey
- New York Islanders
- Pascal Dupuis
- Evgeni Malkin