TORONTO -- Toronto coach Randy Carlyle called it a dagger in the heart. Leafs captain Dion Phaneuf threw himself on his sword.

There was drama and pain aplenty in the Leafs' 4-3 overtime loss Wednesday night that gave the Bruins a commanding 3-1 lead in their playoff series heading back to Boston on Friday.

David Krejci -- with his third goal of the night -- administered the coup de grace at 13:06 of overtime, squeezing a puck through James Reimer on a two-on-one created by Phaneuf's eagerness to pinch in to try and thump Nathan Horton at the other end of the ice.

He got a piece of the Bruins forward but in so doing allowed Krejci and Milan Lucic to head towards the Leafs goal with just Ryan O'Byrne in their way. Krejci used Lucic as a decoy, then snapped a shot past Reimer.

"You can't afford to make mistakes that lead to odd-man rushes," said Carlyle. "We turned the puck over deep in the corner and then we pinched and gave them an odd-man rush and they scored a short-side goal to beat us and that's kind of a dagger, it feels like a dagger after the effort that was put forth by our group.

Said Phaneuf: "I take responsibility for making a bad play. I said that and I don't know what more you guys want me to say. I made a bad play and it cost us the game."

The Leafs now face a potentially decisive Game 5 in Boston, where history and the Bruins are against them.

The Bruins are 15-2 when leading a best-of-seven series 3-1. And Toronto is 2-12-1 in its last 15 games in Boston.

"We knew the circumstances coming into this game," said Lucic. "A lot was on the line and we talked about setting ourselves going into Game 5 so as difficult as these last two games were, it's only going to get harder and we expect the best out of them again."

Patrice Bergeron also scored for Boston, with captain Zdeno Chara collecting four assists. The Bruins power play, 1-for-9 coming into the game, was 2-for-5 on the night.

Krejci now has five goals and five assists in the series, combining with linemates Lucic (0-7) and Horton (3-3) for eight goals and 15 assists.

Joffrey Lupul, Cody Franson and Clarke MacArthur scored for Toronto, whose power-play went 0-for-4.

The Leafs have not registered a home playoff win over Boston since March 31, 1959, when Toronto won 3-2 in overtime.

More than a half-century later, goalies Tuukka Rask and Reimer were both busy in an end-to-end overtime, with Toronto's Matt Frattin hitting Rask's goalpost some six minutes in.

Toronto outshot Boston 48-45 overall and 11-9 in overtime.

"It really felt like we were putting on a lot of pressure," said Lupul. "On the bench, we kind of felt like it was just a matter of time before we got one."

Reimer's wife and mother were in the stands at the Air Canada Centre, often unable to watch for the tension. Phaneuf's fiancee, actress Elisha Cuthbert, was one row behind.

"I try to be as calm as I possibly can but inside your guts are churning. Simple as that," Carlyle said of the overtime.

Reimer got a piece of the puck on the final play, but not enough to stop it from trickling through under his right arm.

"He just beat me," the goalie said. "I thought I got most of it and I had a good read. I just didn't get enough of it."

The Leafs used their speed to great effect and led 2-0 after the first period, only to see the Bruins fight back to take a 3-2 lead in the second before Toronto stopped the slide with a late goal of its own.

"I know that our work ethic was strong. I know we played the game at a pretty high tempo," said Carlyle. "The one thing that's disappointing is we had a two-goal lead."

Tied 3-3, the game hung in the balance to open the third. It was a crucial period with the Leafs either pulling even in the series or going down 3-1.

It was desperate high stakes hockey with players putting their body on the line. Toronto defenceman Mark Fraser, who does not wear a visor, took a Lucic shot to the face with 12 minutes remaining and headed to the dressing room, leaving a pool of blood on the ice.

Fraser was taken to hospital for a CT scan, among other things.

"Obviously they're going to check for any broken bones, basically in the forehead area," said Carlyle.

"Obviously he's going to need some stitches."

Fraser's injury was clearly felt by his teammates.

"The guy's been an absolute warrior. A great teammate for us," said Lupul. "So all our thoughts are with him."

The tense overtime followed a physical 60 minutes. Toronto outhit Boston 71-49 on the night.

"It was a man's hockey game out there," said Carlyle. "There was a lot of energy and a lot of physical play but that's the way the playoffs are played. That's the way it's supposed to be played.

"We just have to find a way now to bottle the positives that we put forth in today's game and bring that for Friday in Boston."

The two teams have combined for 365 hits in four games, with Toronto holding a 200-165 edge.

Inside the arena, the chant of "Go Leafs Go" started before the anthems. Outside, blue-and-white fans came out early to party in the adjacent Maple Leaf Square.

Once again, 2nd Lieutenant Scott Newlands and the 19,708 fans inside bellowed out the anthem to kick off the festivities.

Lupul gave them something to cheer about on the Leafs' first shot at 2:35. Lupul gave the puck to Phil Kessel who raced around the goal and then fed it back to Lupul, who had got enough separation from the Boston defencemen to slap the puck past Rask for his third of the playoffs.

Franson doubled the lead on Toronto's eighth shot of the period with a shot from the point that beat Rask, who had Chara in front of him, at 18:32.

But the Bruins showed their character in the second period, pushing back on the power play just 32 seconds in with an opportunistic Bergeron beating Reimer on a rebound of a screened Chara shot from the point. It was Bergeron's first point of the series and first goal in 14 games.

Krejci was credited with Boston's second goal after a goalmouth scramble at 12:59 that saw Mikhail Grabovski go flying. Chara had helped set the stage with a driving rush.

The Boston power play paid off again with Krejci one-timing a shot past Reimer at 16:39 after a glorious pass from Horton.

MacArthur, who replaced Ryan Hamilton in the lineup, tied it up 44 seconds later with a slapshot from the slot.

Boston's Jaromir Jagr picked up an assist, giving him sole possession of sixth place on the all-time playoff points list (191).