The loss broke Washington's four-game winning streak as it dropped its record to 42-71.
If one looked at the box score, one would think the game was lopsided, but, during the first 7 1/3 innings, it was a well-pitched game from both sides and the score was tied at 2.
But things turned south after that. Right-hander Luis Ayala started the inning and had a tough time getting hitters out. With one out, Matt Holliday hit a bloop double to right field. Disaster struck after that. Ayala walked Garrett Atkins and hit Chris Iannetta with a pitch to load the bases.
Enter left-hander Charlie Manning to face the left-handed-hitting Brad Hawpe, who hit a bloop single to center to drive in two runs.
"I tried to throw a first-pitch slider down and away," Manning said. "It kind of spun out of my hand. It got in on him a little bit and he was able to bloop it over shortstop. It wasn't a pitch I wanted. You kind of want a ground ball in that situation."
Manning then suddenly lost control of his pitches. He walked Troy Tulowitzki to reload the bases and then walked Seth Smith to bring home Iannetta.
"I was missing down. I was missing around the plate. Everything was cutting and sinking. I wasn't controlling it," Manning said.
Two batters later, Saul Rivera was on the mound and hit Willy Taveras with a pitch to send Hawpe home. Tulowitzki then came home when Jeff Baker was issued a free pass. Holliday followed and drove in a run with an infield single.
"I was trying to go inside on Taveras and I hit him," Rivera said. "I tried to do my job and I couldn't do it."
The totals of those two-thirds of an inning were rough. The Nationals allowed six runs on three hits, walked four Rockies and hit two batters. Manager Manny Acta didn't recall seeing such an inning prior to Tuesday's game.
"You always see something new in the game. I don't remember the last time I saw [four] walks and two hit by pitches in an inning," Acta said. "But our bullpen has been very, very good during the second half of the season, so far. They just had an off night."
Nationals left-hander John Lannan pitched his 18th quality start of the season. He pitched seven innings and gave up two runs on five hits.
At first, it looked like he was in line for the win, after the Nationals gave him a 2-0 lead after five innings.
In the second inning, Jesus Flores hit a sacrifice fly to drive in Austin Kearns.
Three innings later, Ryan Langerhans scored on a wild pitch by left-hander Jorge De La Rosa, who pitched seven solid innings and gave up two runs on six hits.
The Nationals could have scored more runs in the late innings, but they didn't capitalize on their chances.
In the seventh inning, the Nationals had runners on first and third with one out. Emilio Bonifacio came to the plate and bounced the ball near third base. Clint Barmes grabbed the ball and tagged Ronnie Belliard, who was leaning too far away from the third-base bag, and then threw out Bonifacio to end the inning.
In the next inning, the Nationals had runners on first and second and one out. Lastings Milledge hit a soft liner to Tulowitzki at short. Tulowitzki was then able to double up Ryan Zimmerman at second base.
"We didn't execute when we had to. We gave away two outs on the bases," Acta said. "When you are playing at Coors Field, you try to get every run that you can."
But the Rockies would tie the score in the bottom of the seventh inning. With two outs, pinch-hitter Ian Stewart took a 1-0 pitch and hit a two-run homer. It was Stewart's first pinch-hit homer of his career.
"It was a fastball down the middle. I knew I had to stay away from him. He stands right on the dish. I knew I had to throw away from him," Lannan said.
But it was the Nationals' relievers who couldn't keep the team in the game when it counted.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.