A 5-1, Game 6 win at Enterprise Center on Sunday extended the Stanley Cup Final and gave Boston a chance to win the championship at home.
"Just the thought of it being over tonight was terrifying," Bruins defenseman Charlie McAvoy said. "We'd come all this way. We come together when it matters, and I think tonight was just a good example of that. We're thankful. We're blessed with a chance to play in Game 7 now."
[WATCH: Bruins vs. Blues Game 6 highlights | Complete series coverage]
Rask made 28 saves, Brandon Carlo scored the game-winner, and Zdeno Chara scored the last of four third-period goals for Boston, which on Wednesday will host a Cup Final Game 7 for the first time.
Ryan O'Reilly scored for a third straight game, and Jordan Binnington made 27 saves for St. Louis, which lost two of its three home games in the best-of-7 series.
Video: BOS@STL, Gm6: Rask makes 28 saves to backstop Bruins
"If you told me four months ago we were going to be in the Final in Game 7, I think I'd take it," Blues coach Craig Berube said. "We've been a good road team. We've won twice up there in this series, so we're a confident group."
Boston was 4-for-4 on the penalty kill and is 17-for-18 in the series. Rask made 12 saves when the Bruins were shorthanded Sunday, including three starting at 2:42 of the first period when Sean Kuraly was serving a delay of game penalty.
"That would have been a kick in the rear if you flip it in the crowd and you don't get through that kill," Bruins coach Bruce Cassidy said. "That was a big part of us being able to settle down."
Marchand scored at 8:40 to give the Bruins a 1-0 lead. He beat Binnington with a one-timer from the bottom of the right circle off a diagonal pass from Pastrnak, who was at the top of the left circle. O'Reilly took a delay of game penalty for shooting the puck over the glass 62 seconds into killing a boarding penalty on Brayden Schenn.
"I'll take blame for that, setting them up on the 5-on-3," O'Reilly said. "It gives them the confidence and a big goal there. ... It shifted momentum."
Video: BOS@STL, Gm6: Marchand goes top shelf for PPG
Rask protected the lead by making 19 saves in the first two periods. He got some help from McAvoy, who prevented a puck from going into the net by hitting it in midair after it went off the post and the goalie's back.
"It's a team effort," Rask said. "The game starts a certain way and then there might be a penalty kill. You know you may have to make a save and you try to keep it tight and hopefully trust your teammates that they're going to get that first goal, get that lead, and then kind of let that ball roll from that."
The Bruins extended the lead to 2-0 at 2:31 of the third period, when Carlo scored with a knuckling wrist shot from the right point that bounced off the ice and went into the net off Binnington's blocker.
Kuhlman, who was playing for the first time since April 30, scored his first NHL playoff goal at 10:15 to make it 3-0, shooting high on the blocker side from the top of the right circle.
Video: BOS@STL, Gm6: Kuhlman buries first playoff goal
O'Reilly scored 1:46 later to make it 3-1 with 7:59 remaining. It was not initially called a goal on the ice, but a review initiated by the NHL Situation Room determined the puck completely crossed the goal line.
Pastrnak extended the lead to 4-1 with 5:54 left, and Chara scored into an empty net to make it 5-1 with 2:19 to go.
"We needed to win a game with good team defense," Cassidy said. "We usually get offense from that and it showed, eventually came around in the third. Same formula on Wednesday."
St. Louis failed in its first chance to win the Stanley Cup since entering the NHL in the 1967-68 season.
"You're not going to win every game," Binnington said. "You're not going to be perfect. We have to regroup and play our game, be disciplined, stay composed and hopefully have a better outcome."
Video: BOS@STL, Gm6: Pastrnak buries Marchand's silky dish
It will be the 17th Cup Final Game 7 since the NHL went to the best-of-7 format in 1939, but the first since 2011, when the Bruins won 4-0 at the Vancouver Canucks.
"We are in a situation that is everyone's childhood's dream here," Boston center Patrice Bergeron said, "and we must realize it."
Video: Clutch Performance: Rask helps Bruins force Game 7
They said it
"We were fighting for our lives, obviously, and when you play desperate normally you see everyone's best game, and I think that's what we had tonight. [Rask] made the big saves when we needed them, but we were able to rely on everyone. We came through." -- Bruins forward Brad Marchand
"I'm really excited to get [Game 7] going. Obviously we would have wished to finish it off, celebrate with our fans and all that stuff, but three or four months ago we'd take any kind of Stanley Cup game. Right now we have a shot at it." -- Blues forward David Perron
Need to know
Blues forward Robert Thomas played for the first time since Game 1. He was minus-2 with no shots on goal playing 9:24. He replaced forward Ivan Barbashev, who was suspended for Game 6 because of an illegal check to the head of Boston forward Marcus Johansson in Game 5. ... The Bruins are the sixth team to win Game 6 on the road to reach Game 7 in the Cup Final. Four of the previous five won Game 7 (Toronto Maple Leafs, 1942 and 1964 (Detroit Red Wings); Colorado Avalanche, 2001 (New Jersey Devils); Tampa Bay Lightning, 2004 (Calgary Flames). Detroit lost Game 7 of the 1945 Cup Final at home to Toronto.
Game 7 of the Stanley Cup Final at TD Garden on Wednesday (8 p.m. ET; NBC, CBC, SN, TVAS)
Video: Bruins force Game 7 with 5-1 win against Blues