The Penguins have a chance to do what they did against the Capitals in 1992 and 1996, when they trailed 2-0 in both series only to rally to win. Washington trailed the New York Rangers 3-1 in the first round before winning the next three games.
"We're right back in it and we have momentum on our side and we'll try to keep it going," said Penguins goalie Marc-Andre Fleury, who made 19 saves.
Sergei Gonchar, Bill Guerin and Ruslan Fedotenko scored in the first for Pittsburgh to quickly turn a one-goal deficit into a two-goal lead. Gonchar was helped off the ice late in the period after a knee-on-knee hit from former Russian Olympic teammate Alex Ovechkin. There was no immediate word about the injury, or how long it would sideline Pittsburgh's most experienced defenseman.
Sidney Crosby had his playoffs-leading ninth goal and an assist, and Max Talbot also scored for the Penguins.
Nicklas Backstrom, Chris Clark and Milan Jurcina scored for the Capitals. Ovechkin, constantly shadowed by defenseman Rob Scuderi, was shut out for the first time in the series. Ovechkin was held to two shots.
Game 5 in the Eastern Conference semifinals is on Saturday in Washington.
Hurricanes 4, Bruins 1
Carolina leads their Eastern Conference semifinals 3-1. Game 5 is on Sunday in Boston.
Jussi Jokinen broke a 1-1 tie with his third game-winner of the playoffs at 2:52 of the third. The Finn then set up Sergei Samsonov for a backhander with 5:29 left, and had one of the assists on Staal's second goal 70 seconds later.
That was Staal's 40th career point in the playoffs, breaking the team record of 39 set by current associate head coach Ron Francis.
Marc Savard scored for the Bruins, who have lost three straight since sweeping Montreal in the first round and winning the opener against Carolina.
If history is any guide, the Hurricanes can start making travel plans for either Pittsburgh or Washington.
They've taken 3-1 series leads twice before in franchise history and have advanced both times. Meanwhile, the Bruins haven't won any of the 21 series in which they've faced such a deficit.