The Spaniards bounced back from their dramatic semi-final defeat by France and led from start to finish as shooting guard Sergio Llull sank 21 points in a flowing performance by the 2009 and 2011 winners.
France, beaten finalists two years ago, and 2003 champions Lithuania clash in a mouth-watering final later on Sunday (1900 GMT).
Looking for their first Eurobasket medal since 1995, the Croatians held their own until midway through the second quarter, with forward Bojan Bogdanovic carrying them with 15 quickfire points.
But Spain, who also finished as runners-up on home soil in 2007, then seemed to move up a gear as Bogdanovic's opposite number Llull sank a barrage of long-range efforts to engineer a 47-38 halftime lead.
Spain pulled away in the second half thanks largely to Memphis Grizzlies centre Marc Gasol, who contributed 17 points and eight rebounds, and Victor Claver's 16 points and six rebounds.
(Writing by Zoran Milosavljevic in Belgrade; Editing by Tom Bartlett)
