On May 20, 2010, during a game against the Toronto Blue Jays, Wakamatsu received his first career ejection. As of June 12, he has a career total of two ejections.
On August 9, 2010, amidst one of the worst seasons in team history, Wakamatsu was fired as Mariners manager. He finished with a record of 127 wins and 147 losses.
On November 8, 2010, Wakamatsu was announced as the new bench coach for the Toronto Blue Jays, under new manager John Farrell.