Al Cowens and Bob Kearney each drove two runs to spark Seattle at home in a season opener for both teams.
The Mariners, who have never had a winning season in their eight-year history, improved their record to 7-2 in openers.
The Mariners took a 2-0 lead in the first off Oakland starter Chris Codiroli, who allowed 12 hits before leaving in the fifth, on RBI singles by Phil Bradley and Gorman Thomas.
Oakland scored three times in the third off Mariners' starter and winner Mike Moore. After singles by Dwayne Murphy and Bruce Bochte, Mike Heath doubled to score Murphy and Mike Davis followed with a two-run double.
The Mariners took a 4-3 lead in the third on RBI singles by Cowens and Kearney. Seattle added two more runs in the fifth on an RBI triple by Cowens -- that knocked out Codiroli -- and a suicide squeeze by Kearney off reliever Keith Atherton.
Edwin Nunez pitched the final two innings for the Mariners to earn the save.
Meanwhile, A's pitcher Mike Norris remained behind in Oakland following his arrest on suspicion of driving under the influence.
The 12-year veteran was ordered back into a drug and alcohol rehabilitation program and barred from team activities by the A's management following the arrest early Sunday.