Andrej Meszaros had missed 21 games recovering from a left shoulder injury.

Naturally, he was rusty and slow to react Saturday to a loose puck during a Bruins power play that began a deadly, 1-2-3 scoring spree in Boston’s 3-0 shutout of the Flyers.

Meszaros failed to clear the zone and Boston scored it’s first goal.

It was the defenseman’s first game since Jan. 24 when he was injured against the Rangers.

“I saw the puck and tried to whack it and there was a stick there, too,” Meszaros said. “I probably should have cleared that.

“Obviously, the goal was my mistake. I should not have let the goal go through me. It was back door.”

He can’t be faulted. It’s going to take Meszaros several games to get his timing and instincts back.