Jamie Moyer (1-2) had a 5.30 ERA in his first three starts, then served up a three-run homer to Chavez in the top of the first inning that put Oakland ahead for good. It was Chavez's sixth career blast off the veteran lefthander and second in as many contests.
Mulder (2-1) protected the lead, allowing two runs and five hits with three walks and five strikeouts. His ERA jumped from 2.14 to 2.33, but he raised his career mark against Seattle to 4-3.
Chris Hammond tossed two scoreless innings and Chad Bradford mopped up in the ninth for Oakland, which has yielded two runs or fewer in five of its last seven games and leads the American League with a 3.13 ERA.
Jermaine Dye collected three hits and an RBI and Eric Karros and Erubiel Durazo each added two hits and drove in a run for the Athletics.