"The more you've been around, the more you understand this is what playoffs is all about," Marchand said. "Nobody expects to win four games in a row. We expect against this group to go a long ways, they have a great team over there. They're going to compete hard, there's going to be ups and downs. We just have to feel comfortable in these situations."
David Pastrnak scored twice, and Tuukka Rask made 38 saves for the Bruins. Pastrnak had one assist through the first three games of the series, which is tied 2-2 with Game 5 at Boston on Friday.
[WATCH: Bruins vs. Maple Leafs Game 4 highlights | Complete series coverage]
"He's a guy we rely on to score and create offense and actually play a good 200-foot game, he's certainly capable of that," Bruins coach Bruce Cassidy said. "It was good to see him score. Scorers, when they don't score, can get antsy. I'm not saying David was there, but we wanted to keep him from going there. Getting his two goals, they get recharged."
Auston Matthews scored twice, and Frederik Andersen made 25 saves for the Maple Leafs, who trailed 2-0 and 5-2.
"The message in our locker room after the first and second (periods) was to keep battling and find away," Matthews said. "There's no quit in this locker room, we gave ourselves a chance but it just wasn't enough."
Video: BOS@TOR, Gm4: Pastrnak nets two 1:35 apart in 2nd
The Bruins went 2-for-2 on the power play; the Maple Leafs were 1-for-3 but did not score until they trailed by three in the third period.
"They were good on their power play, they capitalized on it," Matthews said. "We had our chances there on the power play but we weren't able to capitalize until late, and a lot of times that's a big momentum shift."
Zdeno Chara gave Boston a 5-2 lead at 5:39 of the third period when he scored from the blue line.
Matthews scored on the power play at 11:52 to make it 5-3, and Travis Dermott scored at 13:27 to cut it to 5-4.
"We hung in there after that fourth goal they scored," Rask said. "We were able to be relaxed, got some momentum, run the time a little bit, and that's what we needed. We have enough veterans that we don't panic."
Video: BOS@TOR, Gm4: Chara pots slap shot through traffic
Joakim Nordstrom scored into an empty net with two seconds left to make it 6-4.
"We had the lead and we played well, but obviously they played more aggressively and forechecked a little harder," Chara said. "They got some nice looks there, and we have to obviously go back to video and correct some stuff we could have done better, but we defended well, I thought, this game."
The Bruins took a 1-0 lead at 3:03 of the first period when Charlie McAvoy one-timed a pass from Charlie Coyle at the bottom of the right face-off circle on the power play. Marchand made it 2-0 at 6:38 when he one-timed a pass from Patrice Bergeron at the top of the crease.
Zach Hyman got Toronto within 2-1 at 17:55 when he deflected Morgan Rielly's shot from the point in the slot.
Matthews tied it 2-2 at 1:07 of the second period when he carried the puck over the blue line and shot from the right face-off dot.
The Bruins took a 3-2 lead at 3:16 when Marchand passed to Pastrnak at the top of the crease on a 2-on-1. Pastrnak made it 4-2 at 4:51 on the power play when he one-timed a cross-crease pass from Marchand at the bottom of the left faceoff circle.
"They came out pretty hard and were able to take advantage of some of their chances, they probably came out a little bit harder than we did today," Andersen said.
Video: BOS@TOR, Gm4: Matthews beats Rask with quick wrister
They said it
"They're gamers. They know they haven't been at the top of their game, necessarily, for a few games. Listen, they were ready. They were in the hallway before the game, talking about certain plays. Those guys were dialed in. They're pros. They're top-end players. They're Stanley Cup champions. So those are not guys you worry about very often." -- Bruins coach Bruce Cassidy on Brad Marchand and Patrice Bergeron
"They've got real good players, let's not kid ourselves. But, those two goals tonight, we covered this morning, and we didn't look after it. We've got to fix it. The bottom line is, you can't give those power-play goals up. To me, those are just freebies, those two. Not that they didn't make plays or anything like that, but we weren't in the spots we were supposed to be in. ... It isn't good enough right now. The great thing about it is, series is not over, so we don't have to live with that number. We can still fix it." -- Maple Leafs coach Mike Babcock on a penalty kill that was 0-for-2 in Game 4 and is 6-for-11 in the series
Video: BOS@TOR, Gm4: Matthews taps home PPG for second goal
Need to know
Chara is the second-oldest defenseman (42 years, 30 days) to score in the Stanley Cup Playoffs. Chris Chelios (45 years, 86 days) scored in Game 5 of the 2007 Eastern Conference Quarterfinals with the Detroit Red Wings.
Game 5 of the Eastern Conference First Round at TD Garden on Friday (7 p.m. ET; NBCSN, CBC, SN, TVAS, NESN)
Video: Pastrnak, Marchand lead Bruins past Leafs in Game 4