The Brazilian's curling effort went in off the post after only eight minutes and although Villarreal rallied after the break they could not find a way past keeper Daniel Aranzubia.
New Villarreal coach Ernesto Valverde watched his side slump to their third consecutive defeat and they lie second-bottom in the standings with two points from a possible 15'.
"We had the opportunities, and pushed hard in the second half and I think a draw would have been a fairer result," Villarreal president Fernando Roig told Canal Plus television. "We are very low in the standings and we need to worry about getting some points soon."
Valverde joins Valencia's Unai Emery and Atletico Madrid's Abel Resino in the spotlight with the three sides, all considered top-four candidates, struggling to live up to expectations.
Atletico, also without a win, scrambled a last-minute 2-2 draw at Valencia on Saturday. Valencia are seventh with eight points, Atletico 18th with three.
XEREZ POINT
Leaders Real and Barca have 100 percent records from their opening five matches and top the standings with 15 points each.
On Saturday, Real beat promoted Tenerife 3-0 at the Bernabeu, Barca were 2-0 winners in Malaga, and Sevilla consolidated third place on 12 points with a 4-0 demolition of Athletic Bilbao at San Mames.
Real Mallorca are the surprise fourth-placed side on 10 points after their 3-0 victory over visitors Real Valladolid, earlier in the day.
The islanders made it three wins from three at the Ono Estadi with goals from Nunes, Aritz Aduriz and Borja Valero to continue their impressive start to the campaign.
Deportivo are fifth on nine points with Bilbao. Real Zaragoza climbed to eighth with seven after a comfortable 3-0 win over visiting Getafe with Colombia midfielder Abel Aguilar scoring twice.
La Liga newcomers Xerez earned their first top-flight point but have still to score their first goal after drawing 0-0 at Espanyol. They remain bottom after five games.
"It's not much, but the point will be a boost for morale," Xerez coach Jose Angel Ziganda said.
"The players gave their all and it could be a turning point for us. Next Sunday we'll play with more confidence."
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