Armas, 27, acknowledged that he had problems locating his pitches last year because of his shoulder. He would correct the problem by having minor shoulder surgery last September.
"Last year, every time I threw a pitch, I would finish the pitch and I would have a little pinch [in the shoulder]," Armas said. Sometimes you get away from your release point, trying to get where it doesn't hurt. But I don't have to go through that now."
It looked like Armas could have pitched longer against the Astros, but Robinson is always cautious when it comes to players who are coming off surgery.
"Frank is the boss and you have to respect that," Armas said. In the long run, you have to think it's the first game of the season."
Jose Vidro has played with Armas since the 1999 season, and Vidro was happy to see that his teammate's fastball was consistently in the low 90s.
"He really showed a lot out there. He was around the strike zone all the time. We as a team have to feel very, very pleased because we really need him," Vidro said. "If he can stay healthy for us all year, he is going to be a big difference for us."
The Astros took a 2-0 lead off Armas in the bottom of the third inning. With one out, Craig Biggio doubled off the left-field wall. Outfielder Alfonso Soriano had a chance to get Adam Everett at the plate, but Soriano bobbled the ball after it came off the wall, and Everett scored the first run of the game.
After Willy Taveras singled to put runners on first and third, Lance Berkman hit a sacrifice fly to Soriano to drive in Biggio.
The Nationals made it a one-run game off Astros starter Brandon Backe, when Vidro homered in the top of the fourth.
Backe, who is the third starter in Houston's rotation, was supposed to pitch on Wednesday against the Marlins, but he was pushed back until Friday because of a sore back. He looked healthy as he threw six innings and gave up one run on three hits.
The Astros put the game out of reach in the bottom of the sixth inning against reliever Jason Bergmann, who gave up four runs without picking up an out. Berkman took an 0-2 pitch -- a high curveball -- and hit a two-run home run and, two batters later, former Nationals outfielder Preston Wilson hit another two-run homer, a monster shot over the left-center-field fence.
Bergmann was taken out of the game after he hit Brad Ausmus with a pitch.
"He made two [bad] pitches, that's all. That was a terrible 0-2 pitch. Terrible. With Wilson, he grooved him a nice 2-0 fastball. It just wasn't very good pitches," Robinson said.