There was a period of time on Sunday afternoon in Boston when it seemed as if Rick Nash was going at a different speed than everyone else, and those moments are exactly why the Rangers brought Nash to Broadway in the first place. Big No. 61 in white was flying around the ice, over the boards for every other shift early in the second period, scoring his first goal in the opening nine games of the postseason and setting up what could have — should have — been the go-ahead goal just minutes later. So for all the similarities between this Eastern Conference semifinal with the Bruins and the Rangers’ first-round matchup against the Capitals, the biggest difference is Nash had yet to play a game in this playoff run like the one he played Sunday. When the Bruins come to the Garden tonight to resume the best-of-seven contest in a pivotal Game 3, the Rangers will be facing the same 2-0 hole they faced against the Capitals, a series they won in seven games. But this time, they have seemingly a different Nash on their side. “I’m seeing someone that is trying to take over the game,” said Derick Brassard, Nash’s young centerman both here and during their time in Columbus. “He competes hard and battles and just tries to make a difference. The one thing I know is that he was the best player for us [on Sunday].” There was never more than a two-minute stretch of even-strength time in the second period when Nash wasn’t on the ice. He played on his own line with Brassard and Mats Zuccarello. He played on the third line with Brian Boyle and Taylor Pyatt. He played on the fourth line with Brad Richards and Arron Asham.