The visitors' unlikely hero was former Rangers defenseman Tom Poti who scored one goal and contributed three assists as the Capitals won their second consecutive game to tie the NHL's Eastern Conference quarter-final at 3-3.
Game Seven is scheduled for Tuesday in Washington.
Washington also had goals from two other defensemen, Mike Green and Milan Jurcina, while Russian forwards Viktor Kozlov and Alex Ovechkin both lit the red light. The Rangers scorers were Scott Gomez, Ryan Callahan and Marc Staal.
New York, which had held a 3-2 series advantage and could have wrapped it up with a win at Madison Square Garden, outshot their opponents 32-22. But Washington's rookie goaltender Simeon Varlamov won his third game of the series, after replacing regular netminder Jose Theodore.
The Rangers were forced to play Sunday's game without coach John Tortorella, who was suspended for one game by the NHL after he threw a water bottle at an abusive fan who doused him in beer during his team's 4-0 loss in Game 5 in Washington.
Assistant coach Jim Schoenfeld was behind the Rangers' bench for Sunday's game.
