Ribeiro put in the puck after Troy Brouwer deflected a shot from the blue line.
The Capitals lead the series 3-2. Game 6 is Sunday in New York.
The home team has won every game in the series, with Washington taking the first two and New York pulling even in Games 3 and 4. The Capitals have been fighting history along the way: The franchise has lost eight playoff series in which it has held a two-game lead.
Just the feel for the direction they were headed and what they're trying to do, it just felt that this is a really good thing for this organization. They've got the pieces. We can put something together and go on a run or two and be together for a while, and I'm really excited about that opportunity. The team we have here has an opportunity to win, and that's the most attractive thing.
— Washington defenseman Matt Niskanen on why he decided to sign with the Capitals