Paul McGuinness' side scored twice after the break to see off the Germans after a tight first half contained few openings. Gradually, the Reds assumed control and Max Bauer had to clear off the line to deny Demi Mitchell after a Sam Byrne cross.
Jake Cooper, a guest player from Reading, made the breakthrough when Joe Rothwell's free-kick released Mats Daehli and the Norwegian's centre invited a close-range finish by the big defender. With five minutes left, the lively Mitchell wrapped things with up with an exquisite curling shot after a bold run and one-two with Daehli.
United will face Ajax in the final at 3pm local time after the Dutch team defeated Barcelona on penalties. The hosts shaded a group encounter with McGuinness' youngsters 1-0 on Saturday.
Highlights of the tournament will be screened by MUTV on 22 April.