Taking exception, Desmond shouted in the direction of the Marlins' starter, who threw seven shutout innings.
Immediately, Marlins catcher Jarrod Saltalamacchia went face to face with Desmond, prompting all the players and relievers to spill onto the field.
Order was quickly restored, and the incident defused as quickly as it started.
"The guy pitched a great game," Desmond said of Koehler. "I wasn't necessarily thinking he had intentions of hitting me. You can drill me in the ribs. Drill in the leg or wherever you want. But four or five times missing in or around the head, I'm not claiming it's on purpose, but you've got to be able to control the ball. No big deal.
"It wasn't intended to escalate to what it did -- just heat-of-the-moment stuff sometimes."
Although there was a pile of players swarming around home plate, no pushes or punches were exchanged. Home-plate umpire Marty Foster issued warnings to both benches.
"Guys tend to get a little upset when they get crowded," Koehler said. "But at the same time, they're attacking fastballs out over the plate. It's our job as starters to make sure that they know that that's our part of the plate."
On that specific pitch, Saltalamacchia was positioned down and away, and the pitch ran up and in. Koehler was effectively wild all night. He allowed one hit, but walked five.
"We've been beat too many times late in the game over these last couple series, and that's because we haven't established in," Koehler said of throwing inside in general. "You never want to get beat in late, and that's what's been happening because we haven't been throwing those pitches in."
Saltalamacchia stepped in to protect his starter.
"I just said, 'Hey, man, we weren't trying to hit you, relax,'" Saltalamacchia said.
Saltalamacchia, Miami's main offseason free-agent signing, made a statement to his teammates by his actions.
"We're teammates," the catcher said. "That's what it comes down to. I'm going to protect our guys, regardless if it is the pitcher, the first baseman, [Giancarlo] Stanton or anybody. We're here for each other. We're family. We're going to protect each other. If you see somebody yelling or saying something towards your pitcher, you're going to step in the way."
The incident came with the Marlins, who had lost eight straight, leading 6-0.
Desmond was batting with Jayson Werth on second and one out. Werth had walked on a pitch that was also high and inside. When play resumed, Koehler retired Desmond on a fly ball to center field. The inning ended with Danny Espinosa grounding out to second.
Desmond added that he didn't feel Koehler's pitch was premeditated.
"I meant what I was saying," the Nationals' shortstop said. "This is how I feed my family. Like I said, I'm not scared to get hit, I've been hit plenty of times, never said a word. I just don't like that."
Desmond also realized Saltalamacchia had to step into the mix.
"I've known Jarrod a long time, I wouldn't respect him if he didn't," Desmond said. "This is baseball, you compete and go forward. No hard feelings. That's just the way games go sometimes."