Two of the Nats' miscues came in a six-run first inning that set the tone for Los Angeles to cruise to an 8-3 win.
The Angels have won five straight games and 10 of their last 11 on the road, while the Nationals have lost seven of eight.
"You've got to feed off errors," Angels center fielder Torii Hunter said. "Anytime a team makes an error, you've got to take advantage of it. We try to go out there and take advantage of any mistakes like hyenas."
Mike Napoli ended a 2-for-29 slump with a double, a homer and three RBI, including a run-scoring single in the big first inning. His third-inning home run gave Los Angeles a 8-0 lead.
"It was good to see Nap come out of it a little bit," Angels manager Mike Scioscia said.
A day after a pair of Nationals' errors helped the Angels' late comeback win, Washington's defensive troubles again led to Los Angeles runs. Left fielder Paul Lo Duca -- making his first appearance in the outfield since 2004 -- and first baseman Dmitri Young were each charged with errors during the Angels' big opening inning.
Young also had a throwing error in the sixth and left fielder Willie Harris misplayed a ball in the second.
The lead was more than enough for Jon Garland (7-4), who pitched seven innings, allowing three runs on six hits.
Shawn Hill (1-5) gave up six runs - four earned - on five hits and two errors in the first inning alone. He eventually was pulled after the third, having allowed two more runs.
Hill, who started the season on the disabled list with soreness in his right forearm, has been pitching through pain in his forearm and elbow. Washington manager Manny Acta said Hill would be sent to the Mayo Clinic for another opinion and will likely be put on the disabled list.
Hill said the pain has caused him to alter his delivery on the mound during games and hurt his control. Hill and Acta pointed to Napoli's home run as an example -- Hill was supposed to throw a pitch out of the strike zone, but his fastball ended up over the plate.
"I'm not helping the team, I'm not helping myself," Hill said. "I'm hurting the bullpen, I'm putting Manny in a bad spot. I know it's not just because I'm making poor pitches. I'm just not right right now."
The Angels' Vladimir Guerrero extended his hitting streak to 15 games with a first-inning single, but left after two innings with flu-like symptoms.
Lo Duca left the game during Guerrero's at-bat in the top of the second with lightheadedness. He was taken to a hospital as a precaution.
Wily Mo Pena replaced Lo Duca, and led off the third inning with a home run. Elijah Dukes also had a solo home run in the fourth inning for the Nationals.
Nationals first baseman Nick Johnson had surgery to repair a torn ligament in his wrist Tuesday and is expected to miss the rest of the season. ... Lo Duca, regularly a catcher, started the game in left field for the Nationals, his first stint in the outfield since 2004.