Brandon Backe pitched seven-plus shutout innings, allowing just five hits and four walks while striking out five. So effective was Backe that Washington couldn't get a runner past first base after the fourth inning.
"He was able to throw his pitches for strikes, especially pitch No. 1," manager Manny Acta said, referring to the fastball Backe used to get ahead in counts Sunday. "He had a good slider, too, so we couldn't do much offensively against him."
Backe, one of the league's best-hitting pitchers, hurt Washington with his bat as well, going 2-for-3 with a double and scoring twice, raising his batting average to .345 on the year.
Houston first dotted the scoreboard with a solo home run by Ty Wigginton in the second. The Astros added another the next inning, when Backe doubled and scored two outs later on a Lance Berkman single. Berkman stole second uncontested and scored on Carlos Lee's single, leaving the game at 3-0 in the third.
The Nationals, by contrast, struggled with runners in scoring position, stranding the bases loaded in the second, and then leaving runners at the corners in the third.
Houston delivered the final blow in the seventh when it touched reliever Charlie Manning for two runs, driving the score to 5-0 and putting the game out of reach.
Manning had been on in relief of starter Odalis Perez, who lasted six innings and struck out six. He allowed three runs on nine hits in the outing.
After the game, Acta praised Perez's performance. The veteran southpaw "battled," according to his skipper, posting a quality start in the process.
"He gave us a good six innings," Acta said. "He gave up some hits with two strikes, he was unable to finish some hitters in some innings with two outs, but other than that, he kept us in the game."
For his part, Perez recognized his early-inning struggles, but he still felt good about the outing. The lefty said he's proud of the way the entire starting rotation has pitched this year, and he's hopeful that their continued success can couple with the offense for a strong second half.
Perez also emphasized for the Nationals a need to get key players healthy for the second half of the season.
"Hopefully, looking forward to the second half, you know, [we can] do better, because I do believe that we have some guys on the DL that, we need them," Perez said. "We can play better in the second half."
After the game, first baseman Paul Lo Duca admitted that injuries have been "a little bit" of the problem for the Nationals. A veteran with plenty of success in past stops in Los Angeles and New York, Lo Duca added it will be important for Washington to play with "pride" in the second half if it wants to get better.
"If you like it, every day, losing like this, don't come to the ballpark," Lo Duca said after the game. "You've got to have pride. ... I hate coming to the ballpark and losing. When you win, it's so much more fun."
Lo Duca agreed with Perez that getting some injured players healthy -- both specified franchise third baseman Ryan Zimmerman, set to begin a rehab appearance Monday -- will be key to turning the season around in the second half.
Asked to name his greatest expectation for his squad coming out of the All-Star break, Acta summoned a succinct response -- "better offense and better defense."
"We need a few more guys to step up," Acta said. "Our offense, right now, we're in the bottom in almost every category. ... Our starting pitchers have been tremendous, and our bullpen, it's just too much pressure for them right now to work without any margin for error."