Capitals defensemen Matt Niskanen, left, and Brooks Orpik know it’s time to turn up the heat on opponents like the Bruins’ Patrice Bergeron. (Nick Wass)

As the calendar flips to March, the Capitals are ready to flip the switch.

“We know what to do,” defenseman Matt Niskanen said. “It’s just a matter of doing it. It’s that time of year where we need to start building really good habits.”

With the trade deadline behind them and a first-place showdown against the New York Islanders in Uniondale on Friday, the Capitals’ playoff push has arrived.

But with 18 games left in the regular season, the Capitals are hardly a finished product. Of the 16 teams currently in a playoff spot, the Capitals have the highest goals-against average (3.2). Since Jan. 1, they rank last among all 31 teams in goals against (3.58).

“We’ve been a little inconsistent on the back end, and I don’t know that it’s just the defensemen,” general manager Brian MacLellan said.

The Capitals’ biggest defensive issues have not necessarily been in their own zone, but farther up ice, in the neutral zone.

When the Capitals are at their best, their forwards and defensemen work as a cohesive five-man unit, limiting opponents’ time and space before they reach the blue line.

“If you allow teams to come through the neutral zone with too much speed — if you don’t slow down some of these skilled forwards — they’re going to eat you alive,” defenseman Brooks Orpik said.

The Capitals experienced that during a seven-game losing streak in January, when they were victimized far too often by odd-man rushes and opponents’ transition plays. The Capitals tightened things up while going 9-4-1 in February, but they know there is room to improve.

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“Sometimes we get out of sync with the D and the forwards,” MacLellan said. “It’s going to be important for us, just like last year, to find that neutral zone and to find our defensive zone game.”

A year ago, the Capitals also ranked last defensively among the 16 teams in a playoff spot on March 1.

But in the final 18 games, they produced the lowest goals-against average in the Eastern Conference.

That meant rare lapses, even toward the end of an 82-game marathon.

“The dirty little things that we finally figured out last year,” Niskanen said, “the dirty little things that move a game along and that give your skill a chance to come out, I expect that we’ll start ramping that up over the next few weeks and hopefully hit our stride right around playoff time.”