After Matt Wieters got the green light and gave the Orioles a 2-0 lead on a 3-0 pitch against Jered Weaver in the top of the fifth, Arrieta failed to make it through the last of the fifth.
He had a one-hit shutout and had retired 12 batters in a row heading into that half inning.
But he then gave up five singles, three walks, made an error and threw a wild pitch as Los Angeles rallied for the lead and Matt Lindstrom came in to relieve him with the bases loaded and one out.
Lindstrom did a very good job, getting back-to-back ground outs to the mound to strand the bases loaded and keep the O's deficit at 5-2.
Arrieta's final line: 4 1/3 innings pitched, six hits, five runs (all earned), three walks, five strikeouts and 86 pitches.
His outing tonight is the second shortest by a starter this year and this will be the 10th time in the last 12 games that an O's pitcher fails to record a quality start.
The Orioles have some catching up to do as the game heads to the sixth inning.