BOSTON — Torey Krug flew down the ice with his helmet off, like his big, bad predecessors on the Boston defence from the days of Eddie Shore and Bobby Orr.

He lined up St. Louis centre Robert Thomas and knocked him off his skates, delighting the crowd and sending an unmistakable message to rest of the Blues: The Bruins had woken up from their 11-day layoff, and they were ready to fight for the Stanley Cup.

"I think it gave our team energy, and that's all you're trying to do out there," Krug said after Boston rallied from a two-goal deficit to beat St. Louis 4-2 in Game 1 on Monday night. "Hopefully it gave the guys a boost on the bench."

Sean Kuraly scored to break a third-period tie and assisted on another goal, and Tuukka Rask stopped 18 shots to help the Bruins complete their comeback from a two-goal deficit. Game 2 in the best-of-seven series is Wednesday night.

Forty-nine years after Bobby Orr flew through the air to beat the Blues for the 1970 NHL title, the Bruins got goals from defencemen Connor Clifton and Charlie McAvoy.

Brad Marchand added an empty netter with about three minutes left, but the unofficial clincher came when Krug got up off the ice after losing his helmet in a tussle with David Perron in front of the Boston net.

"You know, you don't want to mess with that guy," Clifton said. "Don't make that guy mad."

Jordan Binnington made 34 saves for the Blues, who haven't been back to the final since getting swept by Boston in 1970. But it was Boston which was struggling with a long layoff — at least early on.

Idle since May 16, when they completed their sweep of the Carolina Hurricanes, the Bruins spotted St. Louis a two-goal lead before snapping out of their slumber.

Brayden Schenn made it 1-0 lead midway through the first period on a third-chance shot. In the first minute of the second, David Pastrnak got sloppy behind the Bruins' net and Schenn was there again, this time to pass it to Vladimir Tarasenko in the slot to make it 2-0.

"I think we can be even better, and we have to be," Perron said.

Bruins coach Bruce Cassidy admitted that the long layoff since the Eastern Conference finals may have left his team rusty.

"The time off, you don't have your edge yet to battle," he said. "We weren't too happy with the way the game was going. We weren't playing our game. We weren't playing to our standard. And I think after the second goal, that kind of woke us up."

The Bruins went on to outshoot the Blues 18-3 in the second period, finishing the game with a 38-20 edge.

"I was pretty much a spectator after that," Rask said.

Just 76 seconds after Tarasenko's goal, Clifton tipped in a pass from Kuraly to cut the deficit to one. And in the middle of the second, on the Bruins' fourth power play of the game, McAvoy came right up the middle and wristed it past Binnington's glove to tie it.

It was still tied five minutes into the third when Noel Acciari, on Binnington's left, made a spin move and swept the puck across the crease to Kuraly. He steadied it with his skate and then poked it in with his stick to give the Bruins their first lead of the game.

"In the second period we stopped skating, turned it over and gave them momentum," Blues coach Craig Berube said. "I thought they were the better team after that."

Notes: Zdeno Chara had a cut on his left arm where he was hit by Tarasenko's shot. He said it required a few stitches but was not a big deal. ... Lil Nas X and Chase Rice, who performed a concert in City Hall Plaza before the game, were in attendance. They both got big cheers when shown on the video board, and the crowd erupted when Rice chugged a beer. ... Members of the Bruins' 2011 Stanley Cup championship team took part in pregame banner ceremonies. Five players on the current roster were on that team: Rask, Patrice Bergeron, Brad Marchand, David Krejci and Chara. ... The Blues scored the first goal for the 14th time in 20 playoff games. They had been 10-3 when scoring first, and 6-1 when leading after the first period. ... Blues D Vince Dunn missed his fourth straight game with an unspecified injury. ... Binnington stopped 83 of the previous 85 shots he faced through one period, dating back to Game 4 of the Western Conference finals.

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The Bruins would be halfway to their seventh NHL title with victory on Wednesday night at home. It would be their first since 2011. They lost to Chicago in the 2013 final.

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Jimmy Golen, The Associated Press