Ryan O'Reilly slammed his stick against the boards in frustration.

He had just sent the puck sailing over the glass for a delay-of-game call while on the penalty kill in the first period of Game 6. He had just handed the Boston Bruins' power play, best in the NHL playoffs since 1981, an opportunity to take an early lead on a five-on-three advantage, which they did on Brad Marchand's goal at 8 minutes, 40 seconds. After the Bruins' 5-1 win over the St. Louis Blues on Sunday to send the Stanley Cup Final to a Game 7 on Wednesday, O'Reilly said his mistake was undeniably a turning point in the game.