Justin Bieber Wet & Shirtless in Seattle to Start Tour

0310-justin-bieber-launch-getty-01Justin Bieber lived up to the hype for his "Purpose" world tour by performing topless, in the rain, on a trampoline and ON one of his dancers ... oh, and he sang some too.

Bieber kicked things off at Seattle's KeyArena with a 90 minute set that featured a torrential downpour which prompted the Biebs to whip off his shirt. The kid knows what sells.

Aside from his songs -- he opened with "Mark My Words" and closed with "Sorry" -- he also wowed the crowd with trampoline acrobatics above the audience.

One of Justin's backup dancers also did some acrobatics ... on Justin. Smart choreography!