The game turned in Washington's favor in the seventh, which overshadowed what was a gutsy 101-pitch performance for Koehler.
After laboring in the first inning, when he gave up a run and allowed two hits and two walks, Koehler settled. Through six innings, he was at 93 pitches, and manager Don Mattingly sent out his starter to face the top two in the Nationals' order. Koehler struck out Michael Taylor, but Rendon singled.
"The way I look at it is, I've got to get that guy out there, the last hitter I faced," Koehler said. "And I've got to do a better job executing in the first. Then we're in a better position."
With Bryce Harper up, lefty Chris Narveson entered.
"We knew he had the first two, and that was going to be the end of the road, with Harper coming up there," Mattingly said. "That was the thinking in that inning. He threw the ball really well. You hate to put him in position where he has a chance to lose it. He threw the ball really well, but that's where we were at in that game."
Harper doubled off Narveson, putting runners on second and third. Daniel Murphy was intentionally walked, and Edwin Jackson inherited a bases-loaded, one-out situation against Jayson Werth, who delivered an RBI single.
"Bases loaded, one out," Jackson said. "You really don't have much room to be too perfect. Ideally, you'd like to come in, get a ground ball and get a double play. I feel like I made a pretty decent pitch to him. He's a great hitter, and he did what a good hitter does. He put the ball in play, and it dropped for him."
The Nationals added insurance with a two-out, two-run single by Clint Robinson.
"Koehler went out and pitched a great game," Jackson said. "It would have been nice to come in and have a shutdown inning for him. The way he pitched, that line definitely doesn't show the way he pitched today."
Koehler did what he's known to do -- battled and gave the club some needed innings, considering in the first three games, the longest outing by a starter was Jose Fernandez going 5 2/3 innings in the second game.
"I didn't really have a good feel in the first," Koehler said. "As the game went on, I felt like I got stronger. I would have liked to execute some pitches better in the first inning, that way I would have given us a better chance to win the game."