Trailing with just seconds left in the third period, New York's Brad Richards scored to tie the game at 2-2 and force overtime.
Richards' power-play goal came with just 6.6 seconds left on the clock, capping off a flurry of action around the net. With five Capitals nearby, the puck came loose from Washington goalie Braden Holtby and Richards fired it past him.
The Capitals took the 2-1 lead earlier in the third period when John Carlson beat Henrik Lundqvist for a power-play goal. Thanks to a late double minor penalty by Joel Ward, the Rangers will begin the overtime period with 1:53 left on the power play. The winner will take a 3-2 lead in the best-of-seven series.