In the top of the ninth, third baseman Yunel Escobar was picked off second base to end the inning -- killing any hope of a go-ahead rally.
With two out and catcher Wilson Ramos at the plate, Escobar broke for third prematurely. Cubs pitcher Hector Rondon calmly threw to third and Escobar was easily tagged out by Kris Bryant.
Why Escobar would be breaking for third is a mystery. He already was in scoring position at second base and the risk/reward of getting to third base -- especially with two outs -- just didn't seem worth the gamble.
Still, the Nationals' miscue in the bottom of the inning was even more costly -- because it probably directly led to the Cubs' game-winning hit.
With one out and Chris Coghlan on first base, pinch-hitter Jonathan Herrera hit a bouncing grounder to second base. Danny Espinosa fielded the ball and threw to shortstop Ian Desmond for the force play at second. But Desmond's throw to first base trying to complete the double play sailed wide and bounced through the opening into the first-base dugout.
Herrera was awarded second base because the ball went in the dugout.
The play was a physical error -- Desmond's 13th of the season -- but it was also a mental error because he had no chance of completing the double play. Desmond, though, defended the decision afterward.
"I'm trying to make a play," he said. "[Coghlan] came in there pretty hard like he's supposed to do. I thought I still had a chance, but I hit the one spot in the fence where it wasn't supposed to.
"But it kind of comes with the territory. You have to take a chance every once in a while. Unfortunately, this time it didn't pay off."
"Desi's trying to make a play out of something that he can't make a play out of," said Nationals manager Matt Williams. "The ball's not hit hard enough to turn two there. He tried to transfer it and throw it quickly, and he threw it wide."
The play was huge -- and not only because Herrera moved up 90 feet on the error.
With a runner on first and two out, the Nationals' outfield would have been playing very deep, the so-called "no-doubles" defense. Instead, all the outfielders had to cheat in a few steps with a runner on second.
With a change in the positioning of the outfield, Addison Russell's game-winning double to right-center might have been just another well-struck out -- and the game would have moved on to extra innings.
Nats center fielder Denard Span believes he would have been able to run down Russell's drive if he had been playing his normal depth.
"Yeah, I think so," Span said. "We were obviously playing in because there was a runner on second. Playing for the ground-ball base hit and trying to throw the runner out at the plate."
Said Williams: "With the wind, we've got to play no-doubles [defense] with a man on first base. But with a man on second base, if we play too deep we have no chance of throwing him out anyway."
John Jackson is a contributor to MLB.com.
This story was not subject to the approval of Major League Baseball or its clubs.