Arrieta (1-0) corralled his first win of the season despite walking five batters. The right-hander yielded three hits en route to his first victory since last June.
The O's built a 5-1 lead before reliever Pedro Strop was tagged for a pair homers to make it close, but Jim Johnson turned in a 1-2-3 ninth to pick up his sixth save of the season.
Tampa Bay starter Roberto Hernandez (0-3) was touched for five runs (three earned) on five hits and three walks with seven strikeouts over 5 1/3 frames.
Lytro unveils camera that can focus a photo after shooting it
Yosemite climber falls 30 feet, suffers major injuries