Maybe it was all the back-to-basics work they’d done in losing efforts finally paying off. Maybe it was the sight of a team they’d dominated for the last couple years. Or maybe they actually can just flip a switch.

Whatever the case, the Bruins last night truly did turn the page and start a new season, dominating the Toronto Maple Leafs in Game 1 of the Eastern Conference quarterfinals. After falling behind on an early power-play strike by the Leafs, the B’s scored four unanswered goals, and probably could have had a half-dozen more, to coast to a 4-1 win at the Garden.

“We have (a switch) in the back,” deadpanned Dennis Seidenberg, nodding to the players’ lounge. “We just turned it over.”

He was, of course, kidding. While it was hard to truly believe in this team when it kept losing important games, it’s undeniable the Bruins were starting to show signs of their old selves. After a healthy scratch, Milan Lucic was ramping up his game going. The fourth line was dominating shifts. The team as a whole was more physically and emotionally engaged.

And last night, they put it all together. The B’s got goals from Wade Redden, Nathan Horton, David Krejci (1-2-3 totals and first star) and Johnny Boychuk and, though they did not score in the third period, the B’s protected their lead by continuing to take it to the Leafs.

“The last four games or so we seemed to be turning the corner,” said coach Claude Julien. “As I’ve often said, when you have a winning streak and you keep winning, you sometimes see some things and it takes a while before you start paying a price for it. I think it was the same way with our team (conversely). We were playing better but we weren’t getting rewarded with the wins, but you could see us turning the corner. Today our guys were focused, they were ready. And at the same time, we’ve been here before, there was some experience behind it. And I thought we played a solid game.”

The B’s spotted the Leafs, in the playoffs for the first time since 2004, a James van Riemsdyk power-play goal just 1:50 into the contest, but the B’s pretty much dominated from that point. After missing on several great chances, Redden finally got the B’s on the board at 16:20 when his bad angle shot from outside the left circle broke off goalie James Reimer’s glove and in.

Then came a game-changing sequence at the end of the period. With Dion Phaneuf in the box for slashing Tyler Seguin, van Riemsdyk had a shorthanded bid that hit the crossbar behind Tuukka Rask, bouncing high and out into the zone. Instead of going for the puck, van Riemsdyk went for a hit and the B’s were able to break out with speed. Redden fired a shot and with 11.7 seconds left on the clock, Horton deflected it past Reimer. The play was reviewed to see if Horton’s stick was too high, but the goal was upheld.

If van Riemsdyk’s shot was a couple of inches lower, maybe, maybe it’s a different game. But after falling down 2-1, the Leafs didn’t put up much of a fight, at least not in a hockey sense.

“I just thought we self-destructed,” said Toronto coach Randy Carlyle.