Halfway through a season in which the Rangers have struggled to create and maintain an identity, the club’s cup is half-full rather than half-empty. For yesterday afternoon’s 4-1 victory over the Capitals — in which the Blueshirts dominated the final 50 minutes — likely represented the Rangers’ most effective three-zone, lockdown performance of the season. “I think there are still parts of our game that everyone would like to clear up, but I think that we’re getting there,” Derek Stepan said after his team’s fifth win in the last six matches boosted the Blueshirts to 13-9-2. “This was one where we were really good from the middle of the first period on, but it wasn’t a great 60 minutes. “That’s what we’re trying to do, to play a perfect 60 minutes,” added Stepan, whose goal at 11:31 of the first negated a softie yielded by Marty Biron to Steve Oleksy just 2:16 into the match. “We haven’t gotten there yet so we’ll keep working on that.” The Rangers were outstanding defensively, both up front and on the back end. Ryan McDonagh, paired again with Dan Girardi most of the game, excelled in his match against Alex Ovechkin. The Blueshirts were strong on the forecheck and in the neutral zone as well. If this were an important one for the Rangers, who have games in Buffalo, Winnipeg and Pittsburgh before their next at the Garden, it was almost a critical one for Brian Boyle, reinserted into the lineup after being a healthy scratch on Friday.