Ferrer remained on course for a third Valencia title with a comfortable win over a player he will team up with next month to help Spain defend the Davis Cup against the Czech Republic.
Ferrer made it four wins against Almagro this season even though his opponent had three break points in the sixth game of the second set.
Ferrer broke Almagro's serve in game 11 and also saved a fourth break point in the final game before taking a 6-3 7-5 win.
Ferrer will meet Ivan Dodig, who was a 6-2 7-6 (8/6) winner against fellow Croatian Marin Cilic.
Jurgen Melzer and Alexandr Dolgopolov set up a semi-final meeting with victories over David Goffin and Marcel Granollers respectively.
Melzer beat Belgian Goffin 7-6 (9/7) 6-4, despite serving seven double-faults.
Ukrainian Dolgopolov defeated Spain's defending champion Marcel Granollers 6-0 6-2.