Haren admitted he was a little tired when he took the hill.
"[I felt] a little tired at the beginning, especially," he said. "I felt fine physically, but as I was warming up and stuff, it was just a little tougher to get loose. Even the first inning or two was kind of a battle for me."
If it was a struggle for Haren, it didn't show in the results. He gave up one run on five hits while walking none and fanning six. He earned his eighth win of the season and fourth in his last five starts. He also notched his sixth quality start since coming off the disabled list July 8, and improved to 3-0 with a 1.04 ERA in four starts in August.
"As the game progressed, my stuff got better and better," Haren said. "My cutter was real good; I worked it in on lefties a lot. I didn't throw quite as many splits tonight, and my fastball got better as the game went along."
The only blemish on Haren's line came on a Brian Bogusevic solo homer in the fourth. It was only the fourth homer Haren has given up in his last eight starts. Prior to that, he had given up 19 long balls in his first 15 starts on the season.
"Haren pitched a heck of a ballgame," Nationals manager Davey Johnson said. "After closing [Saturday] and all the stuff he went through a couple days ago, I was counting on him to give me six innings. He came in after five and I thought I was going to have to go to the bullpen … but he said he felt fine and he went out and pitched a great sixth inning."
The Nationals' offense was finally able to get some hits with runners in scoring position, but they still left 12 men on base and only put four runs on the board despite 14 hits.
Washington's scoring came on an RBI double by Ryan Zimmerman in the first, an infield single by Tyler Moore in the sixth and RBI singles by Ian Desmond and Denard Span in the ninth.
But the Nationals had several other chances throughout the game.
They threatened for more in the first but failed to capitalize. With runners at the corners and one out, Wilson Ramos grounded into a 5-4-3 double play.
In the second, they had runners at second and third with nobody out but again couldn't score. Cubs starter Chris Rusin was able to induce a Scott Hairston swinging bunt in front of home plate, then struck out Haren, and got Bryce Harper to hit a tapper back to the mound to escape the jam.
Rusin acknowledged that while he wasn't sharp, things could have been worse for the Cubs.
"I couldn't find my two-seam [fastball] today, but I was able to find some other pitches to get me out of jams," he said. "[I] just made a couple mistakes that cost me, but I was able to get out of some jams."
In the eighth, Ramos was stranded at third after hitting a leadoff double off reliever Pedro Strop.
"We were lucky to get two runs in the last inning," Johnson said. "We had  hits. We had so many opportunities."
Desmond and Span, who drove in the last two runs, said it's frustrating to squander so many opportunities, but they're glad they had enough to win Tuesday night.
"Some of the ways we were finding to get out were unbelievable," Desmond said. "A lot of chances, that's the good part. I mean, a full-swing ball that stops right in front of the plate, a popup, I mean stuff like that. Usually those balls get fouled back or whatever [and] you get another opportunity. But that's the way it's going."
"It's not frustrating, because obviously we're getting guys on base, so that part of it is not frustrating," Span said. "The part that we can't get them in is frustrating. The name of the game is scoring runs, and we had opportunities earlier in the game to blow the game wide open and we didn't do it. But thank God we were able to get some more opportunities later on in the game to give us a few more insurance runs going into the ninth inning."
Drew Storen and Tyler Clippard combined for two scoreless innings to get the ball to Rafael Soriano, who picked up his 32nd save of the season despite allowing a solo homer to Donnie Murphy.
With the win, the Nationals gained a game on the Reds and are now 9 1/2 games behind Cincinnati for the second National League Wild Card spot with 37 games remaining.
Washington also improved to 55-15 when scoring at least three runs in a game this season. The issue for the Nationals now is making sure they score enough to win going forward.
Desmond said jokingly that perhaps it's as simple as Johnson telling them exactly where to hit the ball.
"Davey actually told me during the pitching change [in the ninth inning], 'Hit a ground ball through the four-hole and Bryce will come around and score,'" Desmond said. "And I hit it and was like, 'Wow, why didn't you lay it out like that for me all the rest of the year?"