Jim Johnson completed the three-hitter by getting the final three outs for his ninth save. The Orioles have won seven of their last nine games while the A's have dropped seven of eight.
Chen was brilliant not allowing a runner to reach third base. He struck out five and walked two. This was the longest start of Chen's career. Chen went 7 2/3 innings on May 10 against Texas last season.
The Orioles broke a scoreless tie in the seventh inning as J.J. Hardy lead off against Tommy Milone (3-2) with a single that A's right-fielder Josh Reddick bobbled for an error allowing Hardy to go to second. After an out, Steve Pearce drove him in with a sharply hit ball past diving A's shortstop Adam Rosales.
Baltimore added two runs in the ninth against Oakland reliever Ryan Cook on an error and sacrifice fly.
Milone gave up six hits and struck out five while allowing the unearned run.
The Orioles had chances early but Milone worked out of trouble.
Milone worked out of a first-and-third jam with two outs in the first inning and continued to get the critical outs when he needed them. After he gave up a lead-off double to Pearce in the fifth, Milone retired the next three Orioles batters to keep it scoreless.
It was the first three-error game for the A's this season.. Injured Oakland slugger Yoenis Cespedes (hand) went 2-for-3 with a three-run homer and a walk in his second rehab game on Friday night with Triple-A Sacramento. A's manager Bob Melvin said Cespedes was scheduled to play in the field on Friday night, DH on Saturday and, if all goes well, will be activated on Sunday. ... The A's are slated to send A.J. Griffin (2-1, 4.50) to the mound on Saturday to face Orioles starting pitcher Chris Tillman (0-1, 5.23). Griffin has never faced the Orioles. Tillman has one previous career start against the A's (May 27, 2011), allowing one earned run and six hits in 4.1 innings. ... The Orioles have not won a season series against the A's since 1998. ... The A's celebrated the 40th anniversary of the club's 1973 World Series title - the second of three consecutive championships - on Friday before the game with an autograph session for fans. The celebration will continue before Saturday's game with a pre-game on-field reunion honoring the members of the 1973.