The Toronto Maple Leafs left themselves little room for error after consecutive ugly road losses to open their first-round playoff series with the Boston Bruins.

With their backs now firmly planted against the wall as they return to TD Garden for Game 5, that margin has dropped to zero.

The Leafs trail the Bruins 3-1 in the best-of-seven Eastern Conference quarterfinal following Thursday's disappointing loss on home ice, where things initially appeared to be lining up in Toronto's favour.

Bruins centre Patrice Bergeron — the heart of a ferocious top line that did almost anything it wanted in 5-1 and 7-3 victories in Boston — was a late and surprising scratch for Game 4 with an upper-body injury two days after the Leafs won 4-2 at a thunderous Air Canada Centre to get back in the series.

But it was a lifeline they failed to grab in a crushing 3-1 loss that saw Toronto carry the play for long stretches, only to be done in by a lack of finish, too many pedestrian performances, and some stunning defensive miscues that led to two goals against on odd-man rushes.

"When you're down 2-0 (in a series), then obviously your margin for error is very slim, right?" Leafs defenceman Ron Hainsey said in the wake of Thursday's defeat. "You can play two great games and not get the breaks, and tough luck."

Toronto now needs a victory Saturday to keep its season — one that included franchise records for points (105) and wins (49) — alive and force a Game 6 back home on Monday.

"We're a tight-knit group," Leafs winger Mitch Marner said. "We don't want to leave each other early.

"We're having a lot of fun in this locker room."

There hasn't been as much fun on the ice, however, where Marner has been by far Toronto's best forward with a goal and four assists.

The team's other young stars have, for the most part, failed to deliver.

Auston Matthews scored the winner on a setup from William Nylander in Game 3, but both have been held off the scoresheet otherwise.

Boston's No. 1 line, meanwhile, has been lights out. David Pastrnak has 11 points (four goals, seven assists), Brad Marchand has seven (two goals, five assists) and Bergeron, the other member of the trio when he's healthy, has five assists.

One positive for the Leafs up front is they should have centre Nazem Kadri back Saturday now that he's finished serving a three-game suspension for a dirty hit on Tommy Wingels in the opener.

"It's going to be nice," said Marner, Kadri's usual linemate along with Patrick Marleau. "He brings a lot of skill. He's going to be eager to get back in."

Kadri, speaking to reporters in Toronto on Friday for the first time since the suspension, said he delivered the dangerous hit because he felt Wingles was "taking liberties" with a previous hit on Marner. Kadri said he disagreed with the severity of the suspension and that he didn't intend to hurt Wingels, otherwise "it could have been a lot worse."

"Was it worthy of a suspension? I definitely think so," he said. "I think the three games was a little harsh."

Along with the Bruins' dominance up front, the Leafs are also losing the battle in the crease.

Frederik Andersen, who set a club record for goalie wins in the regular season with 38, allowed Torey Krug's soft shot through a screen to put his team on its heels just 28 seconds into Thursday's game.

He also gave up three goals on five shots before getting pulled in Game 2, surrendered two suspect efforts in Game 3, and has a .880 save percentage in the series compared to Tuukka Rask's mark of .926.

"We're in a simple situation — you win, you get to play again," Leafs head coach Mike Babcock said. "You don't win, you don't get to play again. To me, that's worth digging in for. I think we can go into Boston and win a game. I really believe that.

"We're going to need a game out of our goaltender, and we need to have all hands on deck."

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