Chen gave up back-to-back singles to Michael Morse and Adam LaRoche leading off the top of the second inning. They moved up on Ian Desmond's grounder, but Chen struck out Tyler Moore.
On the verge of escaping the jam, Chen induced a ground ball from Xavier Nady, who began the night hitting .150 with five RBIs. Third baseman Wilson Betemit ranged to his left to field the ball, but he bounced a throw to first baseman Mark Reynolds, who couldn't scoop it cleanly.
Nady was credited with an infield hit and an RBI, and LaRoche scored on Betemit's error - his 10th of the season and eighth at third base.
Betemit also has an error at first base and one in left field.
Reynolds committed two errors last night at first base, but he's deemed a better fielder at that corner.
The Rays and Giants began the night with 60 errors to tie for second-most behind the Orioles.
Update: Edwin Jackson has retired the first 12 batters he's faced, and he leads, 3-0, after Adam LaRoche's leadoff homer in the fourth inning.
Chen turned in his worst start against the Nationals on May 20, when he allowed six runs and eight hits in 4 1/3 innings. So far tonight, he's been charged with two earned runs (three total) and five hits in four innings.
Chris Davis is in an 0-for-26 slump. He lined out to LaRoche to end the bottom of the fourth.
Update II: Jackson lost his perfect game and no-hitter in the fifth. Adam Jones reached on Ryan Zimmerman's error - it easily could have been ruled a hit - and Betemit grounded a single into right field with one out.
Jackson still has his shutout, however. Mark Reynolds struck out with runners on the corners, Nick Johnson walked to load the bases and Steve Pearce popped up.
Darren O'Day replaced Chen, who allowed three runs (two earned) and six hits in five innings, with two walks and four strikeouts. He threw 90 pitches, 62 for strikes.
Manager Buck Showalter wants Chen to make his next start on regular rest, which might explain why the left-hander is done after 90 pitches. And O'Day hasn't pitched since June 17 in Atlanta.
In two starts against the Nats this season, Chen has allowed eight earned runs (nine total) and 14 hits in 9 1/3 innings.
Update III: Adam Jones hit his 19th homer of the season to break up Jackson's shutout bid in the seventh inning. Betemit and Reynolds singled off him with one out, but former Oriole Michael Gonzalez got pinch-hitter Ronny Paulino to line into a double play.
Betemit froze a few steps off second as shortstop Ian Desmond made the catch and raced to the bag.
Fans booed Gonzalez when he was introduced. He got the last laugh.
Nationals 3, Orioles 1.