Ryan O'Reilly of the St. Louis Blues celebrates his third-period goal on Monday in St Louis, Missouri. Photo: AFP

Ryan O'Reilly scored twice, including the game winner, to lift the St. Louis Blues to a 4-2 victory over the Boston Bruins and level the Stanley Cup final series at two games each on Monday.

O'Reilly scored the go-ahead marker off a rebound of an Alex Pietrangelo shot halfway through the third period to break a 2-2 deadlock and snap the Bruins' playoff road winning streak at five games.

St. Louis came out blazing from the opening puck drop and never trailed, scoring twice in the third period to break open a tight-checking game four at Enterprise Center in the NHL best-of-seven series.

"Our team responds pretty well to things," said Blues coach Craig Berube. "We knew what we had to do tonight to be a better team."

Boston was hoping to take a stranglehold 3-1 series lead. Instead, they struggled to find offense and were outshot 38-23 overall. Their last loss on the road was game three of the quarterfinals against Columbus.

Russian Vladimir Tarasenko and Brayden Schenn also scored while rookie goaltender Jordan Binnington stopped 21 shots for the Blues, who killed all three of their penalties ­after allowing four power-play goals in Game 3. 

The Blues were blown out 7-2 in Game 3 but they are now 7-2 in games after a loss in the playoffs.

Needing a quick start, St. Louis got it. O'Reilly won a loose puck from Danton Heinen behind the net and beat Rask with a wraparound at the far post for a 1-0 Blues lead 43 seconds into the game.

"We were relentless tonight. We didn't stop for 60 minutes," Berube said.

Charlie Coyle and American Brandon Carlo, with a shorthanded tally, scored for Boston and goaltender Tuukka Rask, of Finland, stopped 34 shots for the Bruins, who lost star defenseman Zdeno Chara for a good chunk of the game after he took a puck to the face. 

Boston coach Bruce Cassidy said Chara had to be stitched up and would probably need some dental work to fix the damage. 

Game 5 is on Thursday in Boston.