Prior to the 1999 season, the Mariners signed Lampkin to a two-year contract for $1.55 million to back up Dan Wilson. In Seattle, Lampkin worked with baserunning coach Vince Coleman not on his own baserunning but to learn to "anticipate what the good base-stealers do." Although injuries limited his playing time in 2000, he played well enough in his first two seasons to earn a $1.2 million contract for the 2001 season. The 2001 Seattle Mariners tied a Major League record for the winningest season in history and Lampkin saw his first postseason action, getting a hit in the 2001 American League Championship Series.