St. Louis Blues’ David Perron (57) tries to move the puck between Boston Bruins’ Patrice Bergeron (37) and Matt Grzelcyk (48) during the first period in Game 1 of the NHL hockey Stanley Cup Final, Monday, May 27, 2019, in Boston. (AP Photo/Michael Dwyer)

ST. LOUIS — Bruce Cassidy figures sometime before the puck drops for Game 3 of the Stanley Cup Final, the Boston Bruins’ first line will get together.

Brad Marchand, Patrice Bergeron and David Pastrnak will talk about what hasn’t gone right so far in the series against the St. Louis Blues and what they need to do better. Maybe assistant Jay Pandolfo will show them some video clips for good measure.

“They’re students of the game where they see an opening,” Cassidy said Thursday. “Listen, we’re in the finals. These are good players they’re playing against every night, so they’ve got to find that little edge and I suspect they’ll work hard to do that in Game 3.”

One of Boston’s biggest strength through the first three rounds of the playoffs has been virtually nonexistent so far against St. Louis. Marchand, Bergeron and Pastrnak have zero even-strength points against the defensively sound Blues and will look to break out on the road in Game 3 on Saturday to try to put the Bruins up again in the best-of-seven series.

“We need to capitalize,” Bergeron said in Boston. “For us, it’s about being better. We’ve dealt with this this whole playoffs against different lines. It’s no different. We know how we can play.”

How they can play is pretty darn dominant. They were responsible for 23 of the Bruins’ 32 goals going into the final and exploited matchups against offensive trios similar to the Blues’ top line.

That success hasn’t materialized — yet — against the Blues, who have tried to get the shutdown defense pairing of Jay Bouwmeester and Colton Parayko against Marchand, Bergeron and Pastrnak as much as possible. In the first home Cup Final game in St. Louis since 1970, nothing can be said to be certain except a jacked-up atmosphere Bouwmeester and Parayko sticking to that line like glue.

Cassidy gave St. Louis credit for defending well while also predicting his top line won’t be held off the scoresheet 5-on-5 forever.

“Usually if they check well, get pucks back, they’ll get some odd-man rushes against offensive lines,” Cassidy said. “If they support the puck close together, they’ll get their chances. If they’re able to separate down low against those man-to-man type of defenders, they’ll get some chances. They got a few. They haven’t finished yet. I wouldn’t say that that line has been dormant by any means.”

This is dormant by their standards. Perhaps that’s why Pastrak’s answer to what he and his linemates could do better was, “Obviously, maybe produce more?” That actually starts in the defensive end with getting the puck back and going on the offensive.

“I think executing a little better in our zone — I think it starts there,” Bergeron said. “We have to play a little bit more our way, our style.”

That style won’t be easy to get do because the Blues get the last line change at home and can dictate the matchups. Coach Craig Berube likes going power on power and leaning on Bouwmeester and Parayko to fill the role they have all playoffs.

“They skate well both those guys and just don’t give them a lot of room,” Berube said. “It’s a very good line. It’s hard to handle them for sure. They do a lot of things well. So far it’s been pretty good, but we’ve got to continue to do that. It’s a tough line to defend.”

That’s preaching to the choir for Toronto, Columbus and Carolina — the teams Boston bulldozed through to get to this point. This is the first time this postseason Marchand, Bergeron and Pastrnak haven’t been able to get on track.

Pastrnak believes the key is getting to loose pucks and producing more chances, which this line certainly is capable of doing.

“We want to spend more time in O-zone and always be stronger on the puck,” Pastrnak said. “Once we get to the O-zone, just try to hang on to the pucks and get those second opportunity pucks back to us.”

Because Schwartz, Schenn and Tarasenko are already responsible for three goals in the series, Cassidy expects Berube to try to put them on the ice against the Bruins’ first line as much as possible in St. Louis. He also thinks his guys are prepared and eager for that.

“It’s a big challenge for Bergy, March and Pastrnak,” Cassidy said. “They’ve been up to it. I don’t imagine that will change.”