Champions Barca host unbeaten leaders Real Madrid at the Nou Camp on Monday and third-placed Villarreal seized their chance to cut the advantage held by the big two before the eagerly-anticipated "Clasico".
Zaragoza, who sacked coach Jose Aurelio Gay on November 18 and gave former Mexico boss Javier Aguirre the task of avoiding relegation, remain rooted to the bottom with just eight points from 13 matches.
Pablo Osvaldo's superb volley gave Espanyol a 3-2 win at Atletico Madrid that cemented the Barcelona-based club's hold on fourth, two points behind Villarreal, while Sevilla squandered the lead and lost 3-1 at home to Getafe and stay in seventh.
Former Spain international Senna put Villarreal ahead in the ninth minute at the Romareda with a crisply-struck drive that flew through a crowd of players and fizzed past goalkeeper Leo Franco into the top corner.
Cazorla added a second nine minutes later with a clever lob and Brazilian Nilmar put the game beyond Zaragoza's reach with a neat finish in the 65th.
Zaragoza defender Matteo Contini was dismissed moments before Nilmar's goal after picking up a second yellow card.
"We need to do a huge amount of work," Aguirre, who struck the dugout in frustration after Villarreal's third goal, told a news conference.
"We have not had much time yet to work... but the reality is that we have only taken a point from two matches (since I took charge)."
TOUCHLINE CLASH
Atletico fell behind at a chilly Calderon when the referee ruled Jose Antonio Reyes had handled in the penalty area and Espanyol captain Luis Garcia thundered the spot-kick in off the underside of the crossbar.
Tiago levelled for the home side on the stroke of halftime, roofing the ball after his initial header was saved by Cameroon keeper Carlos Kameni.
Joan Verdu fired Espanyol back in front shortly after the break only for Sergio Aguero to level after he was played in by strike partner Diego Forlan.
Atletico keeper David De Gea got hands to Osvaldo's powerful volley with just over 10 minutes left but could only divert the ball up and into the net.
Atletico coach Quique Sanchez Flores was sent to the stands in added-time after clashing with Garcia on the touchline and had to be restrained by Kameni and other players and officials when he tried to confront Garcia again after the final whistle.
In Seville, Mali striker Frederic Kanoute struck for the home side in the 31st minute at a half-full Sanchez Pizjuan when Ivory Coast midfielder Ndri Romaric hooked the ball across the goal for his African compatriot to sidefoot past Jordi Codina.
A first-time effort from Getafe striker Miku crashed back off Andres Palop's crossbar just after the break before Manu del Moral beat the Sevilla goalkeeper from the penalty spot in the 57th and Miku added a second three minutes later.
Pedro Rios made sure of the three points when he pounced on a loose ba
