ST. LOUIS — Patrice Bergeron wins the faceoff and Jake DeBrusk retrieves the puck for Torey Krug, who waits just long enough for Bergeron to set up and shoots it at his stick for a textbook deflection goal.

This is the Boston Bruins’ masterful power play at its nearly unstoppable best.

When the Bruins go on the power play, it’s poetry in motion on the ice that comes from a combination of detailed coaching and planning, high-end talent and exquisite execution.

Boston scored with precise efficiency on all four of its power-play chances in a 7-2 rout of the St. Louis Blues in Game 3 and is the biggest reason the Bruins lead the Stanley Cup Final 2-1 going into Game 4 Monday night.

“It’s just the creativity and guys stepping into certain roles, certain spots, and we fill in for each other,” Krug said. “When we’re on and we’re in sync, we’re a really dangerous unit.”

Toronto, Columbus and Carolina already figured that out in the first three rounds, and St. Louis needs to develop a solution or this series will be over quicker than Krug can move the puck.

Boston’s playoff-best power play has converted on 35.9% of its opportunities and could be the first unit to finish over 30% in the postseason since the 1981 champion New York Islanders.

“We just have a lot of different abilities and talents out there,” puck retrieving ace Brad Marchand said. “We’ve been together for a while now, so we’re comfortable with communicating and trying to look for different things. With Torey back there making the plays that he’s making, we get lucky sometimes.”

This has nothing to do with luck.

Bruce Cassidy is a power-play mastermind who can spot trends and flaws as well as any coach in the NHL. After the Bruins scored on two of their 10 power plays in Games 1 and 2, he noticed a hole in the Blues’ penalty kill, made some adjustments and, boom, Boston scored four power-play goals ... on four shots.

“Bruce does a great job of giving us cues that if this player does this, this is the option that we’re going to have and the opportunity that we’re going to have to score a goal,” said Krug, who joined Hall of Famer Denis Potvin as the only defensemen to record at least four points in a Cup Final game.

“We’ve been able to, after 10 power plays through two games, point out some things. Without giving it away, we’re trying to take advantage of it now.”

Cassidy said his power play operates differently from a lot of other hockey teams because it relies more on puck movement down low than a blast from the point.

Blues penalty killer Ryan O’Reilly noted the Bruins worked more from Krug at the point in Game 3 and it caught them off guard.

Here’s how they did it:

(asterisk)Bergeron’s tip was a set play Cassidy drew up off a faceoff win that players executed to a T.

(asterisk)David Pastrnak’s backhand came after a Bergeron-to-Krug point-to-point pass and Krug finding him inexplicably wide open in front.