Trailing three games to one, the hard-skating Leafs probed the Bruins from all angles to quiet the yellow-and-black crowd of 17,565 — the Bruins' 156th consecutive sellout. But down 2-0 two minutes into the third period, Boston charged back to threaten the Leafs and pepper James Reimer.
The Bruins outshot Toronto 19-4 in the third period and 44-33 on the night.
Game 6 is scheduled for Sunday night in Toronto with Game 7, if needed, Monday in Boston.
Tuukka Rask, who had faced 95 shots in the previous two games, was immense in the Boston goal but could not get all of Bozak's shot after a Bruins miscue at the Toronto blue-line allowed the speedy Leaf to race in midway through the second period for a short-handed goal.
An opportunistic MacArthur padded the lead at 1:58 of the third, taking advantage of a Boston turnover before racing past defenceman Johnny Boychuk and beating Rask.
At the other end, Reimer was as reliable as a Swiss watch. He ranged from quietly efficient to spectacular, especially as the desperate Bruins tried to get back in the contest. And he got some help from his crossbar in the third after a Boston shot was tipped.
Reimer was finally beaten at 11:12 of the third when Bruins captain Zdeno Chara snapped in a shot after the line of David Krejci, Milan Lucic and Nathan Horton bottled the Leafs up in their own end. Boston had been pressing hard and Toronto could not clear the puck. It was Krejci's 11th point in four games.
The goal brought the crowd alive. A Bozak penalty for delay of the game with 3:48 remaining further cranked up the tension but Toronto killed it off.
The Leafs were hanging on by the end. Captain Dion Phaneuf, pilloried for his role in the Bruins' winning overtime goal Wednesday night, looked exhausted and possibly playing with an injury.
The Leafs have now won two of the three games at TD Garden and will be looking to bring some of that success home.
Boston, meanwhile, will be looking for a way to stop the Leafs from dictating the pace. And to refocus its offence.
Krejci, who came into the game with five goals and five assists, did not manage a shot on goal in the first two periods. Neither did linemate Lucic.
Coming into the game, history was against the Leafs.
Toronto was 1-13 all-time in best-of-seven series in which it trailed 3-1. Boston, meanwhile, was 15-2 lifetime in best-of-seven series in which it had held that lead.
Plus the Leafs came into the game with a 2-12-1 record in their last 15 games in Boston.
After being penned in their own end for the opening minute of the game, the Leafs came at the Bruins hard.
Rask was up to the task, snagging a MacArthur blast and anything else that came his way as the Leafs buzzed the Bruins' end.
Toronto was outshooting Boston 10-4 at the 10-minute mark, using its speed to come at the home side from all angles — largely silencing the fans in the process. The Bruins, meanwhile, looked to slow the Leafs down with hits. Lucic and Krejci treated defenceman Carl Gunnarsson like a Swedish crash test dummy on the same shift, sending him flying into the boards.
With a little more than three minutes remaining, Toronto's Mikhail Grabovski pulled out one of his party tricks. Stationed behind the goal, the slender Belarusian flipped the puck over the goal and then sidestepped Boychuk on the edge of the crease, looking to bat the puck into the net from mid-air. Rask caught it, however, to end the magic act.
Toronto outshot Boston 19-8 in the first period and the Bruins were lucky not to leave the ice trailing. It helped that Boston won 18 faceoffs and only lost three in the period.
Fourteen Leafs had shots on goal in the first period, compared to seven Bruins. The red-hot Krejci and linemate Lucic weren't among them.
The question was how long Boston would stay dormant if the Leafs didn't turn their pressure into goals.
The Bruins had a chance early in the second but Reimer stopped Patrice Bergeron without yielding a rebound. But Toronto began to turn the screw again.
Midway through the period, Bergeron had another glorious chance, coming from out from behind the goal. But as he looked to stuff the puck into what seemed like an open goal, Reimer somehow managed to get a toe to it.
Toronto finally solved Rask shorthanded at 11:27, when Bruins defenceman Andrew Ference was unable to keep the puck in the Toronto zone and the speedy Bozak beat him to the puck. His shot trickled through Rask, who almost had it.
Ference might not have been on the blue-line for the power play had veteran Wade Redden been healthy.
The goal seemed to wake Boston up. Bergeron had another good chance later in the period but could not get the puck past Reimer's leg in a goal-mouth scramble. Then Reimer had to use his glove to deny Jaromir Jagr after the veteran powered his way out of a tangle of bodies on the boards.
Still the Bruins seemed off the game, with defenceman Adam McQuaid racing after Nikolai Kulemin after the Leaf knocked him flying at the Boston goal. Chara then mixed it up with Ryan O'Bryne after a melee in front of the Toronto goal.
Boston outshot Toronto 17-10 in the second period, trimming the Leafs' overall edge to 29-25.
The Bruins have had difficulties closing out series in recent years, although it did not stop them winning the Cup two years ago.
In 2011, they were beaten in possible Game 6 clinching games against Montreal and Tampa Bay but went on to win Game 7. In 2010, they needed six games to dispose of Buffalo (after being up 3-1) before blowing a 3-0 lead and losing in seven to Philadelphia.
Boston's record in non-Game 7 elimination games under coach Claude Julien was 3-6 going into Friday's game.
"I'm going to try and make it 4-6 tonight," Julien said dryly after the morning skate.
Toronto had a different idea.
NOTES — Going into Game 5, James Reimer had faced 163 shots to 147 for Tuukka Rask ... Matt Bartkowski filled in for veteran Bruins defenceman Wade Redden, who has an undisclosed injury ... It was 43 years ago to the night that Bruins legend Bobby Orr scored his flying Stanley Cup-winning goal against the St. Louis Blues.