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
"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."
