Pineiro (4-3) surrendered two runs in the first inning on a Bobby Higginson homerun to right field, but limited to Tigers to just three hits through the next seven innings of work.
Boone's blast, his 10th of the season, was his third in the last two days. It came off of hard-luck Detroit left-hander Mike Maroth in the fifth to put the Mariners up 6-2.
Maroth (0-9) became the first pitcher to lose is first nine decisions of the season since Heathcliff Slocumb did so with Boston and Seattle in 1997. He left after five innings having given up six runs on eight hits.
Seattle (28-15) got on the board quickly for the second day in a row. After an Ichiro single to lead off the game, Carlos Guillen belted a ball over the left-center fence for a 2-0 lead.
The Tigers (9-32) tied it up in the bottom half of the inning with Higginson's two-run shot to right field, but while Pineiro settled down, Maroth struggled to shut down the hot-hitting Mariners.
Colbrunn, who got the start at first base while John Olerud got an off-day, led off the second inning with his second homer of the season.
Boone's homer in the fifth was the icing on the cake and, at 6-1, put the game all but out of reach for the anemic Detroit offense.
Arthur Rhodes pitched a scoreless ninth inning to end the game.
Ichiro Sizzlin: Ichiro's 3-5 day at the plate extended his hitting streak to 10-games and raised his average to .318.