Both players had finished at 7-under 277 at the Oitavos Dunes course.
Hoey had four birdies in his first 10 holes on his way to a joint-best 5-under 66. Fernandez-Castano had four birdies for a 67.
Italys Francesco Molinari (68) finished one shot back for third, while Englands Paul Broadhurst (73), Jamie Donaldson (72) of Wales and Mikael Lundberg (70) of Sweden were at 5-under.
Broadhurst led by one going into the round, but started with three bogeys in the first five holes and then had a double-bogey at the par-5 13th.
Hoey denied Fernandez-Castano a fourth career win to earn $208,330.