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BOSTON -- Claude Julien could feel his Boston Bruins improving even though the results didn't show it.

They did once the playoffs began.

Nathan Horton scored the go-ahead goal late in the first period, and the postseason-tested Bruins used a revived offense to beat the inexperienced Toronto Maple Leafs 4-1 in their series opener Wednesday night.

"There were some signs probably the last four games or so (that) we seemed to be turning the corner," Julien said. "We were playing better. We weren't getting rewarded with wins."

The Bruins had lost seven of their previous nine games, never scoring more than three goals. They played six games in the last nine days of the regular season. Two games in the final week were postponed because of the Boston Marathon bombings and the search for suspects.

So after two days off and a new series starting, Julien believed his players' minds and bodies were refreshed.

"It's been draining for players to deal with that stuff," Julien said. "We're all sentimental to what happened to this city. It was just a matter of turning the page and getting a fresh start from the regular season.

"I think, mentally, that was a big difference. I think that's why you saw a big change in our team. We've been through this as a group."

The Bruins still have 17 players who were on the team that won the Stanley Cup in 2011. The Maple Leafs are in the playoffs for the first time since 2004 and have 15 players making their postseason debuts.

"It's a new experience for a lot of guys," Toronto forward James van Riemsdyk said. "That's a telltale sign how different the level is and how things can come back to bite you."

Game 2 is scheduled for Saturday night in Boston, where the Bruins have won six straight against the Maple Leafs.

The Bruins' late-season skid dropped them to the No. 4 seed in the Eastern Conference.

That set up a first-round matchup with fifth-seeded Toronto, the first time the teams have met in the postseason since 1974. The Maple Leafs lost four of their last six regular-season games.

Their shaky play continued Wednesday after van Riemsdyk gave them a 1-0 lead in the first two minutes. They never scored again.

"We just self-destructed," Toronto coach Randy Carlyle said. "We didn't do a lot of things right. I've never seen so many people fall down with nobody around them with situations with our group. Like we said, we know this going to take more than an ordinary effort, and tonight it wasn't good enough effort."

Wade Redden also scored in the first period for Boston, and David Krejci and Johnny Boychuk added goals in the second.

"That was a tough one to lose, especially with the start we had," Toronto's Nazem Kadri said. "Undisciplined turnovers played a factor, as well. We are just killing ourselves when we do those types of things."

Toronto took a 1-0 lead on a power-play goal by van Riemsdyk just 1:54 in. Redden tied it at 16:20. Horton gave the Bruins a 2-1 edge 3:28 later.

Redden, obtained from St. Louis on April 3, took a shot from the top of the right circle. Horton, sidelined the previous five games with an upper-body injury, lifted his stick and deflected the puck past goalie James Reimer.

After video review, it was determined that Horton's stick stayed below the crossbar.

"To get that one was huge going into the second," Redden said. "We didn't really let off the gas, I don't think, a whole lot. We kept going at them and got a few more big ones."

Van Riemsdyk had opened the scoring after Cody Franson fed a pass to him from behind the goal line.

Redden tied it with a slap shot from the top of the left circle that went between Reimer's left arm and left pad.

After Horton gave the Bruins the lead, Toronto had a good chance to tie it, but Tyler Bozak, who missed the previous two games with an upper-body injury, was stopped on a breakaway by goalie Tuukka Rask at 8:40 of the second period.

Krejci extended the lead at 10:25 when he gathered a loose puck in the crease, spun around and put a 15-foot shot past Reimer.

The Bruins made it 4-1 just over three minutes later on a shot from the right point by Boychuk over Reimer's left arm.

New England Patriots owner Robert Kraft, watching from about 20 rows behind the team benches, waved a towel in celebration of the Bruins' most productive offensive performance in 10 games.

"You just try to be consistent in what you're doing, and some days it goes in more than others," Boston's Andrew Ference said, "I think the generation of chances is always (something) you try to be constant in."

Boston nearly had two more goals, but video review showed that Tyler Seguin's shot early in the second period hit the crossbar, and that Patrice Bergeron jammed the puck into the net midway through the third after it had been covered by Reimer.

Game notes

The Bruins are 21-4-3 against the Maple Leafs in their last 28 meetings. ... CRich Peverley was a healthy scratch for the Bruins after playing 47 of their 48 regular-season games. ... Former Bruins forward Phil Kessel is scoreless in five games against Boston this season. He led Toronto with 20 goals and 52 points.