Sean Kuraly was one of many Bruins to score Saturday night in St. Louis. (Jeff Roberson/AP)

St. Louis had waited 49 years for another Stanley Cup finals game, and everyone from Jon Hamm to Patrick Mahomes to Pam from “The Office” (Jenna Fischer) was at Enterprise Center on Saturday night to support the Blues. And what may have been the most star-laden crowd to attend a hockey game there witnessed a St. Louis team that was overwhelmed not just by the Boston Bruins’ big-name players but also their supporting cast in a 7-2 rout.

Through three games, the Blues have kept the Bruins’ top line of center Patrice Bergeron and wingers Brad Marchand and David Pastrnak off the score sheet at even strength, but it hasn’t mattered much. Boston has a 2-1 series lead because of its depth, following a trend of recent Stanley Cup champions.

In all three games, the Bruins’ fourth line has scored, and while center Sean Kuraly’s goal in Saturday night’s game was ultimately just one of seven, it came with just 10 seconds left in the first period to make it a 3-0 deficit at intermission. Perhaps evidence of their frustration, the Blues took costly penalties — and that’s where the Bruins’ stars were able to capitalize. Bergeron, Pastrnak and defenseman Torey Krug scored on the power play.

“It’s about time we get going,” Pastrnak told reporters in St. Louis. “The whole playoff, every line had their games and that’s the biggest key for us, that so far every game there was another line and that’s how the team works.”

Boston’s transformation into the deepest team of this postseason started with its addition of third-line center Charlie Coyle, acquired from the Minnesota Wild for forward Ryan Donato and a fifth-round draft pick Feb. 20. The Bruins dealt second- and fourth-round picks to the New Jersey Devils less than a week later for winger Marcus Johansson. With his first-period goal in Game 3, Coyle is tied with Bergeron and Marchand for the team lead with eight postseason goals. Johansson had the primary assist and later scored Boston’s fourth power-play goal to give him 11 points in 18 games.

“I think it’s tough to play against," Johansson said last week. “It wears them down. We don’t take any breaks; we have four lines that can produce and four lines that have stepped up in big moments. We got six [defensemen] that all make plays, and it makes it tough throughout a whole series.”

Even as salary cap constraints make secondary scoring trickier to afford, third and fourth lines have become more sophisticated — not just defensive grinders but skilled insurance for when top lines tend to cancel each other out in playoff series. For the Pittsburgh Penguins teams that won titles in 2016 and 2017, there was first the “HBK" line of Carl Hagelin, Nick Bonino and Phil Kessel, a third line that gave opposing clubs matchup fits, and then a fourth line with veteran center Matt Cullen that could steadily contribute in a limited role. The Capitals’ bottom-six forward corps with third-line center Lars Eller and fourth-liner Devante Smith-Pelly put Washington over the top last season with seven goals each — depth that was missing from the team’s repeat bid this year.

Boston’s Kuraly line plays more than most fourth lines, with Coach Bruce Cassidy deploying that trio (also featuring Joakim Nordstrom and Noel Acciari) more than 11 minutes at even strength in the first three games of this series. There has been speculation that Bergeron is playing through an injury — not uncommon for this time of year — and an added benefit of the Bruins’ blowout win Saturday was that he received extra rest down the stretch.

Blues goaltender Jordan Binnington was yanked in the second period after allowing five goals on 19 shots, the first time he’s been pulled in a game in his young career. The talented rookie doesn’t deserve the blame for Saturday’s result with how often his teammates gave the Bruins power-play opportunities, but he’s started to show some cracks this series. St. Louis Coach Craig Berube told reporters he remains confident in Binnington and just thought “he had seen enough” before pulling him Saturday night.

All of St. Louis had.

“Sometimes it’s not going to go your way," Binnington said. "It’s a long series. We’ve come this far. We have to regroup and come back at them for next game.”

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