A 41st minute Kolo Toure strike, in what was a fractious semi-final first leg at Highbury, has given Arsenal a narrow advantage in their bid to reach their first Champions League final.
The centre back pounced at the near post to redirect Freddie Ljungberg's centre into the Villareal net after Arsenal had dominated the majority of the first half.
Despite their possession it was the homeside's first shot on target, but Villareal had rarely threatened with Juan Roman Riquelme registering their only shot on target from a 30-yard free-kick.
Villareal's discipline let them down at times and they were lucky not to have their captain Quique Alvarez sent off in the dying moments when he hauled down Thierry Henry as the Frenchman was bearing down on goal.
Arsenal pressed for a second and introduced both Denis Bergkamp and Robin van Persie to help the push but one was all they could muster, with Javi Venta denying Bergkamp at the death.
The Londoners, who beat Real Madrid and Juventus in the previous two rounds, have now extended their own competition record to nine successive games without conceding a goal.
The return leg is at El Madrigal next Tuesday and the winners play Barcelona or AC Milan in the Paris final on May 17th.
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