The Stanley Cup finals have been a case of acting and reacting, thrusting and parrying, moving and countering.

What the Bruins did in Game 1, the Blues took away from them in Game 2. The Bruins solved that issue in Game 3, and the Blues did the same in Game 4. Each team has been able to respond to what its opponent has done to win the game before. So what do the Bruins need to do in Game 5?

“Respond,” forward Brad Marchand said Tuesday.

It’s certainly their turn. Through four games, no team has been able to string together wins, and the winning team clearly has been the better team in each game – even Game 2, which went to overtime. Each team has been able to turn the tables on the previous game and reverse course.

That will be the big test for Game 5, and whichever team responds best will be the team that will go to Game 6 one win away from taking the Stanley Cup.

“I think that’s been part of why both teams are in the finals,” Marchand said. “Because we’ve both been able to respond and have good bounce-back games whenever we have a loss or a bad game. And you need that this time of year. Once you go multiple games with bad games or not being able to put it together, it’s when you find yourself in a tight spot. That’s why they’re a good team, they’ve been resilient. We’ve been able to do the same. So we gotta make sure we regroup and get back to work (for the) next one. Hopefully have a big game.”

With the series now having become a best-of-three series, the margin for error is reduced even more. At this point, it could be a very fine line between winning the Stanley Cup or having an offseason of heartache.

“I think you’ve seen the response after a loss from each team,” Bruins Coach Bruce Cassidy said. “So it’s kind of, ball’s in our court now to respond. I don’t think there’s one specific thing (to swing the series). We’ve won the special-teams battle, yet it’s still tied 2-2. I think both goalies have played well. Maybe Game 3 they wanted a few more stops, but I don’t think their goalie was the one who cost them the game. That’s an area both teams would be solid.

“Probably comes down to little details here and there. The inside chances they got (Monday) made a difference, every goal they scored they drove the net, got a second chance. We gotta do a better job with that. When we’ve been at our game we’ve used our speed and skill on the forecheck, created turnovers and got inside as well. So that’s how I see it: who’s willing to get in there and create a little puck luck for themselves and that’s usually what it comes down to this time of year.”

BRUINS DEFENSEMAN Zdeno Chara did not go to the arena Wednesday, 36 hours after taking a puck to the jaw in Boston’s Game 4 loss. Cassidy didn’t talk to Chara and only briefly texted with the 42-year-old defenseman, who has a facial injury that has been reported to be a broken jaw.

The absence of Chara could prove to be the tipping point in a bruising battle between the teams. Boston defenseman Matt Grzelcyk is out with a concussion and St. Louis forward Robert Thomas is out with a suspected hand or wrist injury. Cassidy said Grzelcyk, who practiced in a no-contact jersey Wednesday, is still in concussion protocol and would need to be medically cleared in order to play in Game 5.

Cassidy is looking at Steven Kampfer, who appeared in 35 games this season, or a collection of rookies who would be making their postseason debuts. The one downside to putting Kampfer in is he’s a right-handed shot and Chara is a left, which is why Cassidy said he would consider using seven defensemen if Chara and Grzelcyk both can’t go.

“I think what we shouldn’t be worried about is, can we win without certain guys in the lineup?” Cassidy asked. “Should be a mindset that you can still get it done. How are we going to get it done? That needs to be discussed, how you have to make up for the loss of certain players at key positions. ‘Zee’ and ‘Griz’ have been great on the penalty kill. They’ve been effective on it, a lot has to do with the goaltender and some of the regulars. Now we have to plug someone in there. We got to fix that hole.

“(Chara’s) a shutdown defender, forces guys to go outside. We’ll work to get inside. How you going to fix that? I don’t know if you can all of a sudden. We have to talk about the mentality of boxing out better. That also involves forwards. There’s different things you’ve got to do to support each guy missing. ‘Griz’ is more of a puck mover. How are we going to move the puck better when he’s out of the lineup? Forwards have to support the puck better. Did a good job of that in Game 3. The other night not as much.

“This matchup is not good with ‘Zee’ out, let’s face it. They’re a big, heavy team. You lose that element. … But someone else is going to have to step up and I think we do it as a group.”