Only defensemen Torey Krug (25:26) and Charlie McAvoy (24:06) played more for Boston. The Bruins outshot the Blues 39-21, but they were limited to a lone goal by Jake DeBrusk in the third period.
"[Marchand] rang one off the bar last night. [Bergeron] and [Pastrnak] each had some opportunities at the net," Cassidy said. "They've just got to keep working for their opportunities."
Cassidy admitted the Bruins probably are going to need some production eventually from them, particularly with the power play drying up (0-for-5 in the past two games after going 4-for-4 in a 7-2 win in Game 3).
"We can win games without them scoring. You're just not going to do it forever," Cassidy said. "You need it on the power play. Usually your best players at some point have to come through."
They did when the Bruins were facing elimination in the Eastern Conference First Round against the Toronto Maple Leafs. Marchand had two goals and an assist, Pastrnak had two assists and Bergeron had one goal and one assist in a 4-2 win in Game 6 and a 5-1 win in Game 7.
"I remember our big-time players stepping up massive in that game," McAvoy said. "Torey scored one and then [Marchand] scored another one and we kind of took the game from there. Just our big players came through when we needed them."
The Bruins need their big players to come through again now, but Cassidy cautioned against putting all of the onus on Marchand, Bergeron and Pastrnak.
"We can't force it all on three individuals and say, 'Hey, they've got to score or we don't win,'" Cassidy said. "It's a team game, right? So I get that, that they need to produce at some point. We could use a big goal from them. But we can win without them producing. We have. We've gotten here with secondary scoring."
The Bruins' scoring depth is one of the main reasons they've advanced this far. They've gotten goals from a Bruins-record 20 players in the Stanley Cup Playoffs, including 13 in the Cup Final.
Marchand, who leads the Stanley Cup Playoffs with 21 points (eight goals, 13 assists), has three points (one goal, two assists) in the Final (an empty-net goal, a power-play assist and a shorthanded assist). Bergeron has four points (one goal, two assists on the power play and one shorthanded assist) and Pastrnak has two points (one goal, one assist on the power play).
With their Stanley Cup hopes on the line, Marchand would like his line to produce more but said he knows that trying to do too much can be counterproductive.
"Doing more is probably not what you want to look to do," he said. "You probably want to simplify and just play your direct game. I think last game I tried to get the puck a little bit more and get the puck to the net. And that's really what it's all about. The more pucks you get to the net, the more battles you win down low, the more opportunities you're going to have.
"But I think if you take care of the little details in the game, it will go your way."
