He led the rush into the Capitals zone, carrying the puck into the left faceoff circle before sending a low shot toward the net that bounced off of goalie Philipp Grubauer's right pad.
Rick Nash drove toward the net, and the rebound popped out in front. McDonagh followed the puck, got it back and stick-handled through Washington center Nicklas Backstrom's skates into the slot. He got between the circles and beat Grubauer with a wrist shot over his glove to give New York a 1-0 lead.
"It's always great to have a good start, but you have to get something out of it, too," McDonagh said. "It's a real good feeling for me especially having not had a lot of goals this year. Hopefully it gets me some confidence to continue to jump up and make some plays."
McDonagh said several Rangers were talking about the magnitude of the game, the opponent, the impact of the celebration of Hockey Day in America and the fact that they were playing on NBC during practice Saturday.
"Oh yeah," he said. "We were feeling it."
That's not necessarily surprising when you consider the makeup of the Rangers roster.
McDonagh is one of eight Americans on the roster, seven of whom played Sunday. The Capitals had six Americans in their lineup.
Massachusetts native Chris Kreider made the key play on the winning goal, taking the puck to the net off of a faceoff win by center Mika Zibanejad before finding Mats Zuccarello, who scored.
In addition, Minnesota native Derek Stepan had an assist on McDonagh's goal.
"Ever since I've gotten here I feel like we have had a lot [of American players]," McDonagh said. "Maybe it's a coincidence or maybe not, but we've got a lot of those young players like [Kevin] Hayes, [J.T.] Miller and Kreider who are contributing huge for us. It's also great to see Brady [Skjei] doing it too. A lot of Americans. It's a fun group."