IMO the Kuraly line and Kuraly himself had a huge part in that win. They barely got a mention but they played more minutes by far than any other line and it was really Kuraly that saved Chara's bacon.
The Blues again tried to throw the puck over to Chara's side of the ice in the Bruins end and simply skate around him to recover the puck leaving him chasing the play. But instead of playing below the goal line and outside the circles (the dots really) where he has been getting abused, Chara stayed above the line and inside the dots. Kuraly repeatedly drove right past Chara (the stationary telephone pole) took on the Blues Forward and passed the puck out to Chara where his size actually allowed him to be effective mitigating his slowness at the same time. After the 1st period the Blues did not get much of a shot at abusing Chara. Rask was huge in that 1st period.
Also and maybe even more important, the Blues had been forcing the Bruins so deep in their own end that they could stand up at their Blue Line and could see the Bruins coming up ice from a mile away. Just accosted them at their Blue Line, denying the Bruins entry in their previous wins especially. Instead of adopting a more traditional approach to end to end play the Bruins attacked the Blues at Center Ice as Blues came out of their own end with the Bruin Forwards back-checking and selected defenders banging the Blues off the puck from the front side. Suddenly the Blues no longer could stand the Bruins up at their Blue Line and the Bruins could gain entry. Heck the Blues could not get past Center Ice when they had the puck!
That was a risky way for the Bruins to play and its exhausting because the Forwards have to hustle to catch up and back-check through Center Ice and if the Defenseman double teaming misses his play.....WHOOPS. But they just wore the Blues out.
I will be interested to see if the Bruins can repeat that in Game 7. Its exhausting work. But I actually think the Blues are not that fast other than O'Rielly. They are quick and very dangerous once they get in your end. But they are not that fast IMO. Anyway, I am sure the Blues have something planned for Game 7. But if the Bruins are willing to put in the work again other than the Blues successfully mugging the Bruins all over the ice, not sure the Blues can do much about it.