Less than three hours later, they had been pushed to the brink of playoff elimination.
Brad Marchand scored the go-ahead goal and Tuukka Rask made 31 saves as the Bruins defeated the Leafs 3-1 to grab a commanding 3-1 lead in their first-round series. Boston was minus No. 1 center Patrice Bergeron, who was a late scratch with an upper-body injury, but it didn't matter as the Bruins ground out a victory on a night where some of Toronto's young stars failed to produce on the big stage.
"We were set up pretty good," Leafs coach Mike Babcock lamented. "We didn't take advantage. That's on us."
Torey Krug and Jake DeBrusk had the other goals for the Bruins, who can clinch the Eastern Conference quarterfinal series at home in Game 5 on Saturday at Boston's TD Garden. David Pastrnak added two assists.
"We gave them opportunities and they didn't miss," Leafs forward Mitch Marner said. "Now it's do or die."
Bergeron, part of a top line that combined for 20 points in the Bruins' two home victories to open the series, was a surprise late scratch. Riley Nash took his spot between Marchand and Pastrnak, and played well in the four-time Selke Trophy winner's absence earlier this season.
"It doesn't matter (if Bergeron's out)," Marchand said. "You play the same way."
Marchand snapped a 1-1 tie for Boston with 3:05 left in the second after the Bruins were called for icing. Leafs coach Mike Babcock put his top line, centered by Auston Matthews, out hoping to pounce on a tired group, but Nash won the draw to Adam McQuaid, whose clearing attempt up the boards skipped past Toronto defenseman Jake Gardiner. Pastrnak moved in on a 2-on-1 with Marchand, faking a shot to draw the overaggressive Nikita Zaitsev to him before feeding his linemate with a slick pass for a wide-open net.
The Leafs had a number of chances earlier in the period to go ahead, including Mitch Marner's breakaway off a stretch pass from Morgan Rielly that Rask turned aside with the blocker, but were unable to get one by Rask.
Boston then made it 3-1 at 4:17 of the third. David Krejci blocked Travis Dermott's shot and raced the other way on a 2-on-1 before finding DeBrusk, who beat a helpless Andersen after Roman Polak failed to block the pass across.
"We had a breakaway and a good 2-on-1, and we got nothing out of it," Babcock said. "Both their 2-on-1s ... they buried and we didn't make good plays on them to help our goalie out. In the end, that's the game."
The Bruins stunned the Maple Leafs just 28 second into the game to quiet an electric Air Canada Centre when Krug's snapshot from the sideboards found its way past Nash and Plekanec in front before glancing in off Andersen's shoulder.
"It's one I've got to fight to see," Anderson said.
Toronto eventually got going and tied it at 7:43 when Marner fed a pass from his knees that was helped on by Patrick Marleau to Plekanec, who scored his first goal since being acquired from Montreal before the trade deadline.
The Leafs kept coming and nearly grabbed the lead later in the period, but Rask shot out his pad to deny Zach Hyman from in close as Toronto outshot Boston 12-7 through the opening 20 minutes.
Asked how concerned he is that Matthews, who scored the winner Monday, has been mostly quiet, Babcock said some of his youngsters are learning hard playoff lessons.
"I'm assuming he thought he would come tonight and dominate the game -- that's what I thought," the coach said. "I thought the same with (William Nylander). That didn't happen, but the other people you're playing against are pros and they're trying, too, and they're competitive. There's regular-season competitiveness and there's Stanley Cup playoff competitiveness, and it keeps amping up.
"When you leave here tonight as an individual, as a coach, as a player, you've got time to evaluate ... and most guys are pretty honest."
Pastrnak has 11 points in the series (four goals, seven assists), while Marchand has seven (two goals, five assists) despite Boston's top line getting shut out in Game 3. ... Plekanec had three assists in 20 combined regular-season and playoff games with Toronto before Thursday. ... Leafs winger Leo Komarov sat out a second straight game with a lower-body injury. ... Toronto center Nazem Kadri served the final game of his suspension for taking a run Boston forward Tommy Wingels in the series opener. Wingels suited up for the first time since the hit. ... Game 7, if necessary, goes Wednesday in Boston.
Game 5 on Saturday at Boston.