Boston — Tuukka Rask grabbed the final shot in his big glove as the buzzer sounded, sealing the Boston Bruins' stunning sweep of the suddenly powerless Pittsburgh Penguins.

All Rask needed was one goal of offensive support from his Bruins teammates to get Boston back in the Stanley Cup finals.

Defenseman Adam McQuaid snapped a third-period tie, and Rask did the rest as the Bruins beat the Penguins 1-0 to complete a sweep of the Eastern Conference finals on Friday night.

They did it by allowing the NHL's highest-scoring team just two goals in four games — with Rask posting shutouts in the opener and the clincher.

Boston's defense showed it could score as well when McQuaid provided the only offense the Bruins needed at 5:01 of the third period.

"I think first and foremost, we're obviously trying to be solid defensively," McQuaid, who had one goal in 32 regular-season games but two in the playoffs, 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."

McQuaid's goal sparked a chant of "We want the Cup!" from the capacity crowd. At the end of the game, the Bruins were one step closer to another title.

Boston will face either the Chicago Blackhawks or Los Angeles Kings when the Bruins shoot for their second Stanley Cup championship 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.

In the last minute, with goalie Tomas Vokoun removed for an extra skater, the Penguins kept the pressure on Rask. Pittsburgh's final shot, a 40-footer from the center of the zone from Jarome Iginla, was plucked out of the air by Rask.

Seconds later, he was surrounded by ecstatic teammates.

"It's just a scramble," Rask said. "You can't see anything, and people are laying everywhere."

Iginla had turned down a trade from Calgary to Boston before being dealt to Pittsburgh because he thought the Penguins had a better chance to win the Cup, but that turned out to be wrong.

The Penguins never led in the series.

"I just didn't play very well," he said. "That's when you want to play your best for the team."

Iginla and offensive stars Sidney Crosby and Evgeni Malkin got no points in the series.

"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 on a 45-foot slap shot from the right over the Vokoun's glove.

"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, who replaced 2011 playoff MVP Tim Thomas when Thomas decided not to play after last season, was solid again with 26 saves, but didn't have to stop many challenging shots.

"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."

On the winning goal, 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.

Boston'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.

They got no further.

"At the end it felt like not only Tuukka Rask was keeping the puck out of the net, but there was a force around the net," Bylsma said. "There's no question that the performance he put in in this series was elite."

• 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 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.