The last-place Mariners fired manager Don Wakamatsu on Monday, more than halfway through a season that began with hopes of making the playoffs for the first time since 2001.
The Mariners started the day at 42-70, the second-worst record in the AL.
Daren Brown, the manager of Triple-A Tacoma, took over on an interim basis hours before a game against the A's.
M's Fire Manager Don Wakamatsu