Two years ago, it was the Washington Capitals who were frustrated by the defensively conscious, shot-blocking Montreal Canadiens.

Now it’s the Capitals who have a heavily favored opponent flummoxed.

Through 144 minutes 14 seconds of tight-checking playoff hockey, the Capitals have stifled Boston’s potent forwards, limiting them to a total of two goals. It’s the same Bruins lineup that finished the regular season tied for second in the NHL in goals per game and scored five or more goals 21 times.

“They just sit back,” an exasperated Boston Coach Claude Julien said Saturday night. “They play a patient game.”

Some of the Capitals’ success, no doubt, can be attributed to rookie goaltender Braden Holtby, who has stopped 72 of the 74 shots he’s faced. The rest, though, stems from Coach Dale Hunter instilling a commitment to team defense we’re not used to seeing from this team at this time of year.

Washington’s forwards are back-checking with vigor and purpose. The defensemen are steering the Bruins’ forwards to the outside, clearing Holtby’s rebounds and preventing opponents from loitering around the crease.

And everyone is blocking shots.

“That,” winger Troy Brouwer said, “is why we have been able to tie up the series.”

It’s got the Bruins questioning themselves, Hunter beaming like a proud father and the Capitals headed home with the series tied at one game apiece. Game 3 is Monday at Verizon Center.

“I thought our defense played solid,” Hunter said. “The forwards came back hard. I basically told them to keep playing the same way.”

Boston’s top line of Milan Lucic, David Krejci and Rich Peverley has no points and only 13 shots on goal in two games. That unit has been matched up against the Capitals’ No. 1 defensive pair of Karl Alzner and John Carlson for almost two-thirds of its minutes.

Boston’s second line of Brad Marchand, Patrice Bergeron and Tyler Seguin has also been shut out.

“They sit back and get into their 1-4, and if you want to get cute in the neutral zone, then you’re not getting the puck” into the offensive zone, Julien said.

Evidence of the Capitals’ commitment to defending was on display everywhere in Game 2.

The Bruins fired 44 shots on Holtby. Twenty six of them, however, were launched from beyond the circles. Two came from the half wall.

“I know I don’t ever have to cheat because you see the plays we’ve been making on passes across the crease — they’re nonexistent,” Holtby said. “The [defensemen] have been solid, so I can play the shots honestly, challenge a bit more — that’s big for us.”

The Capitals blocked 27 shots Saturday, 19 more than the Bruins blocked.

“It’s something we’ve been working on, especially in the second half of the season,” forward Brooks Laich said. “It’s something that we wanted to be a strength of our team in the playoffs, and everybody’s bought in. At times, I think it’s sort of frustrated them. They’re not getting a lot of real good opportunities, and the shots they do make, or get, Braden’s going to save. Other than that, guys are paying the price to block shots. Even guys that don’t traditionally do it are buying in and doing it now, and it’s tough to play against.”

One of those players is mercurial winger Alexander Semin. Although he has yet to register a point in the series, he managed to leave his mark on Game 2 with a pair of crucial plays in overtime. First, he dived to swipe a puck away from Lucic, thwarting a potentially dangerous scoring chance for the bruising Bruins winger. Then, Semin went down to block a shot off the stick of Zdeno Chara, who owns a 108-mph shot, the hardest in the NHL.

“He got a few pats on the back after the game,” defenseman Mike Green said of Semin’s blocked shot. “That’s what we need. Alex isn’t one do that all the time, but when he shows that he’s willing to do it, it brings us all up.”

Captain Alex Ovechkin added: “I think everybody was laughing. But it’s the playoffs. Everybody has to do whatever it takes to win that the game.”

It’s plays like Semin’s that make an enormous impact in playoff games.

The Capitals didn’t understand that in the past. They do now.