That gave Washington its third nine-game losing streak of the year.
Lannan lasted four-plus innings and gave up a season-high eight earned runs, as his ERA soared from 3.40 to 3.81. He found himself in trouble in the first inning, when Garrett Atkins hit a two-run single. It would get worse by the third, as Lannan gave up three more runs. In the fifth, the Rockies batted around and plated six more, three of which were charged to reliever Garrett Mock.
"I just didn't have anything today," Lannan said. "I just wasn't there mentally. ... I don't know what it was. I felt fine in the bullpen. I guess I didn't prepare myself in the right way. I can't describe how I felt, but it wasn't how I usually feel."
Lannan, 23, has pitched 141 2/3 innings this season, but he and manager Manny Acta denied that the southpaw's arm might be fatigued.
Last year, the Nationals shut down Lannan in late August as a precaution because he had tossed more than 150 innings.
"I have my routine, and it hasn't changed," Lannan said. "I'm not tired. I may be tired of losing. It's very frustrating to go out there, and the team goes out there and puts six runs on the board, and I can't continue the ballgame. I'm tired of that. I'm not physically tired."
Acta simply felt that Lannan had a bad ballgame, pointing out that Lannan had a quality start against the Brewers last Sunday. In fact, he had a no-hitter through five innings without having his best stuff.
"I'm not going to be looking for excuses," Acta said. "He is not tired. He just couldn't throw the ball the way he wanted. He couldn't locate the ball. It was up in the zone. It has nothing to do with being tired. You either locate or you don't locate."
The Nationals were only in Saturday's game during the early innings. They tied the score at 2 against former Nationals right-hander Livan Hernandez in the second inning. Ronnie Belliard drove in Lastings Milledge with a single, while Austin Kearns scored on a double-play ball hit by Kory Casto.
The Nationals scored four more runs off Hernandez in the bottom of the sixth inning, highlighted by Belliard's two-run double.
Since being traded from the Nationals to the Arizona Diamondbacks on Aug. 7, 2006, Hernandez has won five of six games against his former team.
"I don't know," Hernandez said. "I can't say anything -- I'm lucky."
The Nationals haven't been lucky at all, as they became the first team this season to lose 80 games.
"It's tough," Ryan Langerhans said. "We can't seem to play all facets of the game on the same night. We try to take some positives from every game. We battled back in that [sixth] inning, but the bottom line is we have to start getting it done and come up with more runs."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.