Arrieta appeared to run out of gas after retiring 14 of 15 batters. Neil Walker hit his second home run off Arrieta, and the next two batters walked.
Arrieta threw 91 pitches, including 54 for strikes.
Chris Jakabauskas replaced Arrieta and stranded two runners.
Arrieta is charged with four runs and five hits, with three walks and four strikeouts. He gave up three home runs, and his ERA stands at 5.79.
Update: The lead grew to 7-4 in the bottom of the sixth on Nick Markakis' single, an error and Vladimir Guerrero's sacrifice fly.
Update II: Felix Pie's two-out bloop single to left increased the lead to 8-4 and produced his fourth RBI of the night. He had three before the game started.