Buffalo coach Lindy Ruff barks during the team's loss Tuesday night in GAme5 at Buffalo. (AP photo)

Closeout time has arrived in the first round of the Stanley Cup playoffs, and the pressure to avoid a Game 7 is squarely on Montreal, Buffalo and Vegas on Friday night.

A tantalizing tripleheader of Game 6 action begins with the Tampa Bay Lightning’s visit to the Canadiens and the Sabres’ trip to Boston (7:30 p.m., ESPN), followed by the Golden Knights visiting the Utah Mammoth in the nightcap.

A series-clinching win would be nothing less than monumental for the Canadiens and the Sabres, whose hockey-hungry markets would love to see the second round again.

No fan base in the league has been hungrier for longer than Buffalo, which went 14 years without seeing a playoff game before these Sabres won their first Atlantic Division title this spring.

They’ve got an even bigger step to take now, however — learning to close out a playoff series. The Sabres barely failed in their first chance Tuesday, losing Game 5 at home in overtime to the resilient Bruins.

Then again, Buffalo’s lineup didn’t have a lot of experience, with just 10 players having previously appeared in an outing with a chance to eliminate an opponent.

“We trusted the process to get to this point,” Buffalo coach Lindy Ruff said. “You’ve got to continue to trust it. It’s a team (that for) a whole year has won together and lost together, but embrace this moment — and somebody for us is going to be a big time player. I can’t tell you who that is, but somebody will.”

Buffalo’s power play continues to sputter: Rasmus Dahlin’s goal in Game 5 was the Sabres’ first with the man advantage in 18 opportunities this series. Buffalo enters Game 6 having converted one of 20 power-play chances against Boston after going 0-for-22 to close the regular season.

The Sabres’ last playoff series victory was in the second round in 2007 against the New York Rangers.

David Pastrnak’s breakaway goal 9:14 into overtime sealed a 2-1 win over the Buffalo Sabres on Tuesday night to keep the Bruins’ season alive.

They’re now back in TD Garden to try to do it again, but it hasn’t exactly been a haven in this series: The Bruins were outscored 9-2 in their home losses in Games 3 and 4.

It’s why coach Marco Sturm said the dramatic Game 5 victory doesn’t make them feel like they’ve cracked the code against Buffalo, even after some schematic changes that went Boston’s way.

The Bruins were 29-11-1 at home during the regular season.

“(Being home) should elevate your game,” Sturm said. “We’re against the wall, so home or away I see it more like we have to bring our A-game. Otherwise we go home, so we’re going to approach it that way. It’s a one-game mission again.”

Buffalo will be down one of its key contributors in this series as it looks to clinch its first playoff series victory since eliminating the New York Rangers in six games of a 2007 second-round series.

Rookie forward Noah Ostlund went down with a lower-body injury in the first period on Tuesday.

Sabres coach Lindy Ruff didn’t reveal what the injury was, but said, “it doesn’t look good.” Ostlund had just returned to the lineup from an upper-body injury in Game 3, in which he had a goal and assist.