SEATTLE — The last-place Seattle Mariners have fired manager Don Wakamatsu.

The team announced the dismissal of the major leagues’ first Japanese-American manager hours before Monday night’s game against Oakland.

Wakamatsu is the fifth manager in the majors to be fired this season. Baltimore’s Dave Trembley, Kansas City’s Trey Hillman, Arizona’s A.J. Hinch and Florida’s Fredi Gonzalez also were dismissed.

Seattle entered the day 42-70, the second-worst record in the American League.

The Mariners added pitcher Cliff Lee, infielder Chone Figgins and outfielder Milton Bradley in the offseason, and began the year with expectations of their first postseason since 2001. Wakamatsu guided Seattle to an 85-77 record in his first season after taking over a team that went 61-101 in 2008.

But a poorly constructed roster has produced the worst offense in baseball and doomed them to 22 1/2 games behind first-place Texas in the AL West.

The Mariners announced 43-year-old Daren Brown, the manager of Triple-A Tacoma for the last three-plus season, is replacing Wakamatsu on an interim basis.

Seattle also relieved bench coach Ty Van Burkleo and pitching coach Rick Adair. The team also released performance coach Steve Hecht.

Roger Hansen, who had been the Mariners’ minor league catching coordinator, takes over as the bench coach. Carl Willis, who was the Mariners’ minor league pitching coordinator, takes on the responsibility of big league pitching coach.

“I have concluded that these changes needed to be made now and that they are in the best interest of the Mariners as we move forward,” Seattle general manager Jack Zduriencik said. “Don, Ty and Rick are all good baseball men, and they have done their very best. But we are where we are. I no longer have confidence that Don, Ty and Rick are the right long-term fit for our organization. New leadership is needed, and it is needed now.”

Wakamatsu was asked last week by The Associated Press how he was doing amid rampant speculation that he would become Seattle’s fall guy.

“I’ll be all right,” the 47-year-old Wakamatsu said. “I’ve been in this game a long time, and I have a lot of people pulling for me — most of all my family.”

He went 127-147 since getting Seattle’s job in November 2008.

Wakamatsu watched slugger Ken Griffey Jr. slump this season to the point the manager finally benched the franchise icon, before Griffey drove home to Florida in early June and retired in a huff without saying goodbye to most in Seattle. Wakamatsu also has had multiple public spats with Figgins, whom Zduriencik signed to a $36 million free-agent contract before the season. The most recent incident was an in-game fracas inside the home team’s dugout between Wakamatsu, Figgins and other coaches and players in full view of half the stadium and a national television audience.

The only support Wakamatsu received publicly was a limited one that came days after he led the Mariners through the worst July in team history — 6-22. On Aug. 3, Zduriencik said: “Don is our manager. Don and I, and his son went out to dinner last night. We had a very nice evening, spent like three or four hours together and talked about a lot of things. We talked where we’re headed with the club, about Don, and Don is our manager.”

But when asked if Wakamatsu will return for a third season as Mariners manager in 2011, Zduriencik was evasive and noncommittal.

“Everybody is evaluated at all times,” he said. “As we go forward, you have to realize there is always an evaluation process going on at all times. You take a week at a time, a month at a time, a season at a time with everyone.”