Cordero blew his fourth save in eight opportunities as the Nationals lost to the Cubs, 4-3, in 10 innings in front of 40,481 fans at Wrigley Field. Washington has now lost five straight games, dropping its record to 9-22.
Cordero entered the ninth inning with a 3-2 lead, thanks to Dmitri Young's two-run single off right-hander Bob Howry two innings earlier. However, Cordero had a tough time finding the strike zone with his fastball.
The first batter he faced, Cliff Floyd, never swung the bat as he walked on four pitches, a free pass that ended up hurting Cordero in the long run.
"Everything I was throwing was running away," Cordero said. "I was probably opening up [mechanically]. Any time you walk the leadoff guy ... it's going to make it tough for me. You never want to do that. Unfortunately, I did, and the results went in their favor. I was mad at myself."
Cordero also had a tough time finding the strike zone with the next hitter, Daryle Ward. Cordero fell behind in the count, 2-0, allowing Ward to fight off some pitches before hitting a single to left field to put runners at first and second.
After Alfonso Soriano flied out to Austin Kearns in right field, Ryan Theriot tied the score at 3 when he singled to right-center field to drive in Jason Marquis, who was pinch-running for Floyd.
"[The leadoff walk] has a high percentage of scoring in baseball," manager Manny Acta said. "When you score three runs a game, you have to play perfect baseball to win. We almost played perfect baseball -- except in the end, when our closer failed today."
Acta acknowledged that he was concerned about Cordero, who is off to one of the worst starts of his career. He now has a 4.70 ERA. Acta said he still has confidence in his closer and that Cordero will continue to save games for the Nats. Acta believes winning a few more games will solve Cordero's problems.
"There's only so much we can do. We'll keep throwing him out there. We don't have other options. And even if we had them -- I mean, this is a guy who has been a premier closer in this league for the last few years, so we have to get him right."
Cordero has not received regular work this season, since save opportunities have been very few. He also is even playing with a heavy heart because his grandmother, Josie, is dying. But Cordero said that the lack of opportunities and his grandmother's illness have nothing to do with his problems on the mound.
"I threw well on Saturday, so I should have been able to do the same thing today. For some reason, I just couldn't get it done," Cordero said. "Just because I'm not getting opportunities, it doesn't mean I shouldn't be able to go out there and get the job done.
"When I'm out on the mound, I'm not thinking about my grandmother. When I'm out there, it's all baseball. Off the field, you think about it."
In the 10th, it was reliever Ryan Wagner who couldn't get the job done, as Ward singled over the drawn-in outfield to drive in Matt Murton for the game-winning run.
The losses continue to mount for the Nationals. They are already 10 1/2 games behind the first-place Mets. They now play a three-game series against the red-hot Brewers starting on Monday night.
"We have to forget about today. Forget about the series and play the Brewers to the best of our abilities," Young said. "We are not on a suicide watch. This is the game of baseball -- 162 games. If we can't handle it, we'll quit. But we're not quitters."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.