Nationals 5, Mets 3 (13). Jacob deGrom, New York's 26-year-old rookie who's been quite terrific this season, faced Washington's Jordan Zimmermann, who is 28 and has been quite terrific for several years.
Zimmermann worked around a Daniel Murphy single in the first, while deGrom retired the Nationals in order. Zimmermann threw a perfect second, and his teammates took the lead in the bottom of the inning when Adam LaRoche doubled and Ian Desmond homered.
New York responded in the top of the third when deGrom singled, moved to second on a bunt, and scored on Murphy's double, cutting the lead to 2-1. deGrom allowed a Denard Span single in the third, but got a double play from Anthony Rendon to end the inning. Zimmermann threw a 1-2-3 fourth, and the Nats restored their two-run margin on a LaRoche double and a Desmond single in the home half of the inning.
Zimmermann was flawless again in the top of the fifth. Washington threatened in the bottom of the inning when Jose Lobaton singled, was bunted to second, and took third on a Span single, but Span was caught stealing second and Rendon flied out to end the inning. The Mets had a chance in the top of the sixth when singles by Murphy and Lucas Duda put runners at the corners, but Juan Lagares struck out to strand them. deGrom walked LaRoche in the home sixth, but struck out the other three hitters he faced in the inning.
Wilmer Flores led off the top of the seventh with a single; Anthony Recker flied out, but Kirk Nieuwenhuis hit for deGrom and singled as well. Drew Storen relieved Zimmermann and promptly threw a wild pitch, moving the runners to second and third. Eric Young Jr. brought Flores home on a sacrifice fly, and Curtis Granderson singled Nieuwenhuis in with the tying run. Vic Black was perfect in the bottom of the seventh, and Tyler Clippard worked a flawless eighth. Span and Jayson Werth both singled in the bottom of the eighth, putting runners at first and second and chasing Black, but Josh Edgin struck out LaRoche and Jeurys Familia retired Desmond to end the threat.
Rafael Soriano set the Mets down in order in the ninth. Familia allowed an Asdrubal Cabrera single and walked Lobaton, then was relieved by Dana Eveland with two outs; Eveland coaxed a Span forceout to send the game to a tenth inning. Matt Thornton and Buddy Carlyle were both spotless in the tenth; Craig Stammen threw a 1-2-3 eleventh, while Carlyle allowed a one-out Bryce Harper single but stranded the runner at first. Stammen walked Nieuwenhuis in the twelfth, but allowed nothing else. Jenrry Mejia relieved in the bottom of the inning and got to face Stammen as the leadoff man; Mejia struck out the opposing pitcher, which would end up helping him escape the jam that would be created by Span and Werth singles.
Since Stammen hit for himself in the twelfth, it was inevitable that he would pitch the thirteenth; he did so effectively enough, allowing a David Wright double and an intentional walk but no runs. Carlos Torres relieved in the bottom of the inning, and the Nats ended the game quickly, as Desmond drew a walk and Harper launched a walkoff homer.
The Nationals are having a very good season - they have the NL's second-best winning percentage so far - and they're doing so despite a very lackluster year from the man who was expected to be their best position player. Bryce Harper has missed about half of the season so far due to injury, and been less than wildly effective even when on the field.
One walkoff home run does not necessarily mean that Harper is going to start wreaking havoc on the league, of course, fun as that would be to see again. But it at least means the Nationals won this game.