David Moyes's side started to pose more of a threat in the second half, with Carlos Martinez latching on to a cross to unleash a powerful effort from outside the box, but his finish was wide of the left upright.
Ibanez doubled the advantage just five minutes later, turning on the edge of the box before rifling the ball towards goal, with a deflection leaving the keeper stranded.
Alberto de la Bella tried to give the home side some late hope, crossing the ball for Fernandez, but he was unable to get himself into position to get a shot away.
The visitors put the win beyond doubt with just moments to spare, though, as Rochina powered the ball towards goal from long range, just squeezing his strike under the crossbar.
The result leaves Granada just outside the relegation zone, two points clear of the drop with one fixture still to play, while Real Sociedad sit 12th.