The Bruins dominated the series and held the high-scoring Penguins to just two goals. Pittsburgh never even had the lead in any of its four losses.
"I think first and foremost, we're obviously trying to be solid defensively," McQuaid said of the defensemen. "It obviously feels good. It feels good to be able to contribute that way when you don't normally.
"You look at so many great efforts we had from guys. The last 10 minutes of the game, guys were all over the ice, doing whatever it took to preserve that goal."
Boston will face either the Chicago Blackhawks or Los Angeles Kings when the Bruins shoot for their second Stanley Cup title in three years.
Chicago leads the Western Conference series 3-1 and can advance to the finals with a home win on Saturday night. If the Blackhawks get there, it will set up the first finals matchup of Original Six NHL franchises since 1979.
"I don't feel like they totally shut us down," Crosby said. "I feel like we got chances, but Rask made some big saves."
McQuaid scored at 5:01 of the final period on a 45-foot slap shot from the right over the glove of goalie Tomas Vokoun.
That unleashed loud chants of "We want the Cup!" from the capacity crowd.
"We were a little sluggish the first two periods," Bruins forward Milan Lucic said, "and we said, `We have to win a period to win a series."'
They did just that.
The top-seeded Penguins were trying to overcome both the disciplined defense of the fourth-seeded Bruins and history. Only three teams had lost a series after winning the first three games. The last was the Bruins in the 2010 Eastern Conference semifinals against the Philadelphia Flyers.
The Penguins felt they were "put together to win the Stanley Cup. That's our expectation from Day One," coach Dan Bylsma said. "You're going to look at this as a missed opportunity."
Pittsburgh was swept for the first time in 47 series. The last team to do it to the Penguins was Boston in 1979.
The Penguins also lost the first three games of their opening-round series last year against Philadelphia before being eliminated in six games.
Rask was solid again with 26 saves, but didn't have to stop many challenging shots. His last save came with his glove at the final buzzer on Jarome Iginla's shot from 40 feet.
"He has been the reason why we're here," Bruins forward Patrice Bergeron said of Rask, who stopped 134 of 136 shots in the series. "We just played our game the whole time. We put a lot of pressure in their zone."
The Penguins had been shut out just twice in their previous 147 games before being blanked twice in the four games against the Bruins. Pittsburgh lost Game 1 at home 3-0.
Holding down Crosby and Malkin was the key.
"He is the best player in the world," Bergeron said of Crosby. "We did a good job with that."
After the game, a calm Rask felt that shutting out the potent Penguins twice wasn't such an overwhelming feat.
"Every game starts with zero," he said, "so you have a chance."
McQuaid scored his second goal of the playoffs after he managed just one in 32 games during the regular season.
"It's obviously nice when you can get a little offense from your defense," he said.
Brad Marchand held the puck along the left boards in the offensive zone and waited for McQuaid to skate up ice. Marchand fed the puck toward the blue line where McQuaid, with no Penguins player close to him, unleashed the winning shot.
There was little sustained offense in the first two periods when Pittsburgh outshot Boston 20-17.
Bosotn's Kaspars Daugavins hit a post at 2:56 of the second period during his first appearance in the series. Daugavins replaced injured center Gregory Campbell, who broke his leg in the second period of Boston's 2-1, double-overtime win in Game 3 on Wednesday night.
At 10:56 of the second on Friday, Vokoun made a save with his right pad against streaking Tyler Seguin from the left side.
The Bruins got this far by beating the Toronto Maple Leafs in seven games in the first round and then taking out the New York Rangers in five to reach the East finals.
Boston rallied from a three-goal deficit in the third period of Game 7 against Toronto just to reach the second round.
"It seems like a lifetime ago," Lucic said. "Without that Game 7, to come back and win it, if it wasn't for that we wouldn't be here right now."
The Penguins topped the New York Islanders and Ottawa Senators to reach the NHL's final four.
- John Krasinski, star of 'The Office' and a native of nearby Newton was in the stands with his wife, actress Emily Blunt.
- William and Patricia Campbell, whose daughter Krystle Campbell died in the Boston Marathon bombings, waved the "Fan Banner," a traditional part of pregame activities.
- Gregory Campbell's father, Colin, was a defenseman on the 1979 Penguins, who were swept by the Bruins. Gregory Campbell gave a wave to the crowd when he was shown on the arena video board.