Unlike some gentlemen who share his line of work, goalie Tuukka Rask has never been one to make excuses, or rationalize, or otherwise try to duck blame that comes his way. When he does something bad, he is his own most withering critic. “It was just awful,” said Rask of his goaltending error-for-the-ages last night that sparked new life in the New York Rangers, who went on to a 4-3 overtime victory, averting a series sweep and forcing a Game 5 tomorrow back in Boston. It will be hard to find a Bruins fan who hasn’t seen what occurred at 8:39 of the second period last night at MSG. Probably seen it multiple times, none any less painful. The B’s had just claimed a 2-0 lead on the latest bit of brilliant precosity by youngster Torey Krug and seemed to have the game and series — and a weekend off — firmly in hand. But then a puck was shot by the Rangers’ Carl Hagelin high in the B’s zone. The shot wasn’t too hard to begin with, and slowed down even more when defenseman Johnny Boychuk got his stick on the puck. Indeed, the puck was barely moving at all as it slid toward Rask. Unfortunately, something very bizarre happened to Rask: He fell down. And sat there in front of his cage watching the puck slide, oh so slowly, just beyond his extended right leg and into the net. The New York fans responded as though they just witnessed the loveliest goal in NHL history. Luckiest was more like it. “That happens to me twice a year in practice, maybe,” said a chagrined Rask. “Focus. I’ve got to be more focused, I think. Just a tough mistake. It looked pretty bad on TV, I’ll bet.” Oh yes, Yes, indeed. Rask actually did have an explanation for how his feet went out from under him. “I just took a step to the side and what I think is there was probably a skate (rut) or something,” he said. “My skate dug in it. That’s what it felt like. I lost my balance and the rest was history.” And once he was sitting, with the puck slowly approaching, what then? “That was just sloppy,” said Rask. “It kind of like freezes you. It’s like, ‘What the heck happened?’ You still have a second to decide whether you’re going to try and scramble and get the paddle down, or try to whack it away. I tried to whack it away.” It certainly wasn’t the only costly blunder by the Bruins, but it was the most important, and the one that will be remembered if somehow this relatively one-sided series starts to go downhill for the B’s. “It’s a game of mistakes,” said Rask. “Every team makes mistakes and every player makes mistakes. You’ve just got to learn from them and move forward. I don’t think a couple of mistakes are going to make us a bad hockey team. That’s just something that happens sometimes. You’ve got to shake it off and move on.”