The Rangers had spent much of the last few days talking about how the dynamic had changed for the better with the trade deadline moves that reshaped the club.

Last night, in one of what will be a string of essential battles down the homestretch to secure a playoff spot, the Rangers just weren’t dynamic enough until the third period, and then when they were, one of a number of critical defensive zone breakdowns proved fatal to the cause.

For after trailing by two goals after two periods, the Blueshirts rallied to draw even on goals by Rick Nash — who had a pair in a bravura performance — and Derek Stepan, only to allow Toronto’s Phil Kessel to break the tie and deal the Rangers an eventual 4-3 loss at 9:39, just 39 seconds after the Blueshirts had tied it.

“The next shift after a goal is so important, and we didn’t get the job done,” said Nash, who was part of the unit on for the breakdown on which Kessel slid home his own rebound after finding himself alone in front of Henrik Lundqvist. “It’s definitely disappointing.”

The defeat leaves the Rangers in a tie for seventh place in the Eastern Conference with the Islanders and two points ahead of the ninth-place Devils, with all three clubs having nine games remaining. The Blueshirts are two points behind the sixth-place Senators, who hold one game in hand. And they’re six behind the fifth-place Leafs, who are at the Garden tomorrow night.

“We’re a desperate hockey team desperate for points, but we had mental breakdowns,” Nash said. “At this point we have to be at our best. We can’t have defensive zone breakdowns. We count on Hank to make the first save; he shouldn’t have to make the next couple also.”