The loss spoiled the effort of Joe Saunders, who worked 6 1/3 innings and allowed three runs (two earned) to put the D-backs in position to win. Arizona is now 4-2 on this 10-game road trip, and both losses have been of the walk-off variety.
"It's a long season, and you're going to have games like that, where you play well but you just don't come out on top," said outfielder Justin Upton, who homered and scored twice. "We're going out there [and] we're playing good baseball. You can't win them all."
The D-backs, though, thought they had this one wrapped up after they grabbed a 4-3 lead thanks to a two-run sixth-inning rally.
And when reliever Craig Breslow managed to wiggle out of a first-and-second, no-one-out jam in the eighth, it seemed like fate would smile on the D-backs.
Then came the bottom of the ninth.
Rookie phenom Bryce Harper led off the frame with a double off the wall in right-center off J.J. Putz.
"I think it was a two-seamer away," Putz said. "I'm not sure where it ended up, but he put a good swing on it."
The closer bounced back to strike out Wilson Ramos and pinch-hitter Rick Ankiel, putting the Arizona on the brink of the win.
That brought Desmond to the plate, and while he was standing on deck, he took the advice of his former manager Frank Robinson.
"He said, 'You have to watch the pitcher,'" Desmond said of Robinson, a Hall of Fame player. "[Putz] was throwing his splits up in the zone, and his fastball was elevated to both guys ahead of me. I knew if I looked for the heater, I would be able to see the split up and be able to react. I was really locked in, and everything clicked for me."
Putz threw Desmond a fastball that the right-handed hitter fouled off, and then the D-backs' closer missed with another heater to even the count.
The next pitch was a 93-mph fastball that missed its spot, and Desmond sent it into the cool Washington night.
"I was just trying to go down and away, and just left it up, middle, middle in," Putz said. "I made a bad pitch, and he hit it a long way. For the most part, I felt like I threw the ball really well, just left one pitch up, and game over."
D-backs manager Kirk Gibson was asked about the fact that both losses on the trip came in heartbreaking fashion.
"So what?" he said. "It's disappointing, but we'll regroup. These guys will be fine. We'll come out and play a good game tomorrow."
They played a pretty good one Wednesday, too, in what was a seesaw affair.
Harper, who made his home debut Tuesday, was in the center of the action, and not for his ninth-inning rally-starting double.
With the D-backs up, 2-1, in the fourth, Danny Espinosa drew a two-out walk and Harper followed with a double off the wall in right to tie the game.
Ramos then hit a scorching one-hopper to second baseman Aaron Hill, who knocked the ball with his glove and it rolled a couple of feet behind him. Harper, running all the way with two outs, never stopped, and Hill's throw to the plate beat him, but Harper knocked the ball out of the glove of catcher Miguel Montero to give Washington a 3-2 lead.
Montero briefly protested the play, claiming that Harper slapped the ball out of his glove.
"We couldn't see it from where we were," Gibson said. "If he does it intentionally, by the rule, he's out. But I didn't see it, and I don't think the umpire saw it as well. Maybe that's what happened."
Montero was more convinced after looking at the replay following the game.
"I thought he went after my hands, my glove, and he kind of hit my glove," Montero said. "If you watch the replay clearly you see that. The umpire said he didn't see it, but it's what it is, whatever. It was a tough play. I did watch the replay, and it clearly looked like he tried to slap it out of my hand."
Regardless, the Nationals took a 3-2 lead on the play.
That advantage lasted just one inning, as the D-backs rallied for a pair of runs in the sixth to recapture the lead at 4-3.