BOSTON — One of the Bruins’ biggest problems today in their Game 1 victory in their Eastern Conference semifinal series was killing penalties.

The Flyers, who clicked at a 27.6-percent success rate in the first round against New Jersey, cashed in on two of five chances against the Bruins at TD Garden. Boston was a perfect 19-for-19 against Buffalo in the first round and killed off Philly’s first two chances today.

“I think we did a pretty good job at it, it’s just tough luck happens sometimes,” said center David Krejci, who was on the ice for one of Philly’s power-play goals.

Chris Pronger snapped the Bruins’ string of perfect penalty killing with a one-timer from the right point after Mike Richards beat Krejci clean on a draw in the left circle. Kimmo Timonen dished the puck over to Pronger for the shot that cut Boston’s lead to 3-2.

Richards then scored a power-play goal that pulled the Flyers to within 4-3 with 7:23 left in regulation by burying a rebound of a tough-angled Daniel Briere shot from the left doorstep.

“It’s just breaking down in front of the net and [me] going to the wrong guy,” said forward Daniel Paille, one of the prime performers for Boston’s proficient penalty kill all year long. “And it goes to the outside guy for a wide-open net. Those are the chances that we were fortunate that didn’t go in against Buffalo that went in today. Obviously, we can help by working on it.”

The Bruins didn’t take another penalty the rest of the day. So next game they can try to start up another streak.