Oakland dropped its first two games of the season and has not lost since, winning eight in a row while building the best record in the majors.
The Athletics pounded out 16 hits and pulled away late while handing the Angels their fourth consecutive loss. Los Angeles, at 2-7, has the worst record in the American League.
After Donaldson gave Oakland a 3-1 lead with his homer, Chris Young contributed a two-run double later in the sixth. Yoenis Cespedes hit a solo homer in the seventh.
A.J. Griffin (2-0) allowed a run on five hits over eight innings to pick up the victory. The lone Los Angeles run came when Howard Kendrick doubled home Josh Hamilton in the fourth.
The loss went to Jason Vargas (0-1), who was touched for five runs on 10 hits in 5 2/3.