In last night’s second period, when the Bruins were on a four-on-three power play, David Krejci carried the puck out of the left corner and locked eyes with Dennis Wideman. Krejci motioned, with a shake of his head to the left, where he wanted the defenseman to go: the front of the net. Given how much swagger Krejci was playing with, Wideman was sure to listen.

“When he’s got it going, the puck finds him,’’ Wideman said. “When he’s got the puck on his stick, he’s dangerous. He seems to find guys.’’

Wideman, usually stationed at the point on the power play, drove to the slot to force a seam in Buffalo’s three-man box. At the same time, after playing give-and-go with Patrice Bergeron, Krejci spotted the Wideman-created passing lane open up.

Krejci faked a shot, then slipped a pass through the lane to Mark Recchi, which Buffalo goaltender Ryan Miller thought would be his last option.

“Krejci rolling across the top, as a righthander, he had a shooting situation,’’ Miller explained. “Recchi would maybe be his last option because he was skating toward him. I got a little locked on trying to hold my ice in case he shot.’’

Recchi slammed a short-angle shot past Miller at 1:01 of the second to give the Bruins a 2-0 lead.

There was little doubt Wideman’s approach to the net helped create the goal. After all, Claude Julien and his staff have only been telling players to go to the net for an entire season.

“It took us 82 games to get it through their heads that it would make that big of a difference,’’ Julien said after last night’s 4-3 series-ending win. “We’ve been preaching that all year. We’re a determined group. Guys are understanding and seeing the results from it. At the same time, if we didn’t have the middle drive and traffic in front of that goaltender, he would have stopped them all.’’

The consensus, from the players to the coaching staff to management, is that the 39-30-13 regular season qualified as a disappointment. Too many down years from important players. In-and-out emotional engagement, the lifeblood of the previous year’s club. An inability to develop consistency in any part of their game. A reluctance of getting their noses bloodied in the danger areas.

But as much as the regular season was an all-around dud, it appears, after one playoff round, that a yearlong malaise might have been the most effective delivery of alarm to the 2009-10 Bruins.

Last night, after booting Buffalo from the postseason before 17,655 at TD Garden to claim a 4-2 series victory, the sixth-seeded Bruins exhaled — there were plenty of held breaths during the Sabres’ empty-net rally — and reflected on the important qualities of the first round. Air-tight goaltending. Good health. Commitment throughout the roster. Resiliency amid adversity.

Qualities that, for most of the regular season, flickered like a light bulb not screwed in quite right.

“It’s nice to see that somewhere along the way, we learned from those tough situations,’’ Julien said. “We’d been through adversity. Poor play. We weren’t always good. The injuries and everything else. You hope that your team grows through the course of the season facing those kinds of situations. I think we did. It was nice to see that we were reaping the benefits of that. Having said that, we just got past the first round. There’s lots more to come.’’

Last night, Tuukka Rask (27 saves) outdueled Miller (28) once more, making his best stop in the third when he dived to smother Jason Pominville’s tying chance. The penalty kill, led by workhorses Johnny Boychuk (3:36 of shorthanded ice time) and Zdeno Chara (3:32) snuffed out the Buffalo power play once more to finish a 19-for-19 run. Krejci and Recchi, two of their go-to offensive guns, scored three of the team’s four goals. The power play, once seen floating to the bottom of Boston Harbor during the regular season, beat Miller twice last night to conclude the series at a 6-for-22 clip.

But perhaps the most significant reason the Bruins are moving on to play either Pittsburgh or Philadelphia was their battle level in the danger areas.

In the first period, after Recchi circled on the right wing to stretch out the Buffalo PK, Krejci showed no hesitation to head to the front of the net. Recchi aimed a shot for Krejci’s stick, and the center tipped the puck past Miller at 13:39.

In the third, with the Bruins leading, 2-1, Krejci padded the lead when he parked himself in front of Miller once more. As Krejci gained net-front position, Miroslav Satan rimmed a pass down the wall for Milan Lucic, who muscled Derek Roy off the puck and spotted his center in the slot. After accepting Lucic’s backhand pass, Krejci wasted little time burying a shot over Miller’s glove at 7:18.

Following a Michael Ryder cough-up on the next shift, Nathan Gerbe slammed a slap shot past Rask only 22 seconds after Krejci’s goal to make it 3-2. But Satan, who beat Miller in double overtime two games earlier, struck once more. This time, after Miller had stoned him on a point-blank shot, Satan regrouped and drove to the far post. Wideman saw Lucic and Satan driving hard and sent a pass out front. The puck skittered past Lucic to the stick of Satan, who buried his shot for his second winner in three games.

Four goals. Pucks and people in front on all of them — two qualities the regular-season Bruins only showed occasionally.

“Sometimes it’s like that,’’ Krejci said. “Sometimes you win in the regular season, then hit a wall. That’s what happened to us last year. Hopefully we learned from that. We don’t know who we’re going to play. We’ve just got to play our game, play hard, and do the same things we did today.’’