The Nationals collected three hits against Garcia, who at one point retired 14 straight batters before Roger Bernadina singled to right in the seventh inning.
"We got one broken-bat hit and one hard-hit ball," manager Davey Johnson said. "It's tough here. We should have swung the bats better. Garcia kept us [off-balance] with a lot of offspeed pitches, but we helped him out by swinging at balls, and that was the story of the day."
Nationals right-hander Dan Haren had his second consecutive quality start, but he ended up losing his sixth game of the season, allowing two runs on eight hits.
The last time Garcia pitched eight innings in a game was September 19, 2006, against the Royals. Garcia was a member of the White Sox at the time.
"I feel pretty good. You have to. They bring me here to pitch innings and I try to do the best I can, man," Garcia said. "[Seven] years ago, I pitched eight innings, you know, I don't really remember, but you've got to go out there and pitch the best I can."
Garcia took advantage of the warm weather by using his split-fingered fastball, shortstop Ian Desmond noted.
"It was like facing R.A. Dickey," Desmond said. "Obviously, R.A. Dickey won the Cy Young. It's no knock against Freddy, but I think the humidity and ... his fingers had a little sweat going on there -- that pitch was pretty unbelievable tonight. He used it a lot.
"We know he is a veteran pitcher. He has done it for a long time and he is experienced. He must have thrown 60 percent split-fingers, which is very out of the ordinary. But we have to make adjustments. It's not getting any easier. We all have to get better. Now, it's no more complacency. It's time to turn it on. Sometimes adversity like this can break teams apart. We are going to stick together, and as a team, we are going to figure it out."
On Wednesday, Ryan Zimmerman hit three home runs against Baltimore. On Thursday, he went hitless in three at-bats against Garcia.
"A knuckle or something. I don't know. If a pitcher's got a good pitch and he throws it as much as he did, obviously you start to look for it and we still can't hit it," Zimmerman said. "It's just one of those nights where he had a really good pitch and he used it as much as he could, and it worked for him."
The Nationals' best chance to score against Garcia, who went eight innings, came in the second. They had runners on first and second with no outs. But Tyler Moore grounded out to put runners on second and third, and both Chad Tracy and Kurt Suzuki flied out to left field to end the threat.
The Orioles scored their first run in the third, when Ryan Flaherty came home on a double by Nick Markakis.
Baltimore then scored its second run in the bottom of the eighth inning, when Nate McLouth touched home plate on a double by Manny Machado.
After the game, Johnson indicated that changes need to be made. He would not say what he had in store for the next game, though getting Bryce Harper and Jayson Werth back in the lineup would be a boost. Both players have missed time recently because of injuries.
"We need to get some guys back that are hurt and some of the young guys are struggling. We will probably make some changes, but that's for another day," Johnson said.