Top seed Ferrer was comfortable in a 6-0 6-1 win over 17-year-old German wildcard Alexander Zverev, while Mayer saw off another home favourite in Philipp Kohlschreiber.
Ferrer required less than an hour to end the stunning run of world number 285 Zverev on the clay courts in northern Germany.
Zverev, the youngest player to compete in the semi-finals of an ATP World Tour 500 event, accounted for seeded entrants Santiago Giraldo and Mikhail Youzhny on his way to the semi-finals, but had his work cut out early against Ferrer.
As had been the case in his quarter-final against Tobias Kamke, Zverev failed to win a game in the first set.
And Zverev was unable to recover on this occasion as Ferrer won all but two of 15 first-service points in the second set to remain on course for a 22nd career singles title.
Mayer is set to contest his first ATP World Tour 500 final after coming through a stern examination of his credentials from seventh seed Kohlschreiber - who, like the Argentine, had not dropped a set prior to their last-four meeting.
The German made a nightmare start against Mayer, who broke in the second game before moving 3-0 ahead.
Kohlschreiber battled back to level the set, only to then be broken at 6-5 down as the Argentine moved ahead in the match.
Mayer again gave up a lead in the second set, having been 4-1 ahead, but made a timely breakthrough on the Kohlschreiber serve to maintain his 100 per cent record against a player ranked 20 places above him in the world.