The Spanish youth international, on loan from Real Madrid, scored with a low shot from outside the area in the fourth minute and although Valencia lived dangerously at times they moved on to 13 points from six games.
Granada, who won successive promotions to return to the top-flight after a 35-year absence, hit the crossbar in the second half but a lack of firepower left them as the league's joint lowest scorers with two goals from six games.
Well-worked goals from Zaragoza's Luis Garcia and Pablo Barrera in the first half had Villarreal on the back foot despite Giuseppe Rossi having levelled at 1-1 with a twice-taken penalty in the 41st minute.
A red card for Zaragoza's Maurizio Lanzaro after 80 minutes lifted them and Hernan Perez headed in from a corner, but Villarreal have now managed only one win from their last eight outings, which includes two defeats in the Champions League.
Mallorca´s 2-2 draw at Osasuna was played against a background of boardroom squabbles, after the club parted company with coach Michael Laudrup in acrimonious circumstances during the week.
The Dane's number two Miguel Angel Nadal took temporary charge of the team with former Athletic Bilbao boss Joaquin Caparros waiting for final approval on a deal for him to take over next week, according to local media.
