Dave Tarpey put Maidenhead ahead after 25 minutes before doubling the lead seven minutes after half-time.
The White Tigers have won just won of their first seven games this season since Lee Hodges took charge of the club for a second time in the summer.
The result left Truro, who made the play-offs last season, in 15th place in the table on six points.
Truro City's poor start to the National League South season continued as they lost 2-0 at leaders Maidenhead United.