Robert Pires gave the visitors the perfect start with a seventh-minute opener, but Valmiro Valdo levelled 10 minutes later.

Uruguay striker Forlan took centre-stage after the interval, with a brilliant 30-minute treble ensuring Manuel Pellegrini's men took away all three points.

Former France midfielder Pires set Villarreal on their way by slotting home low past Osasuna goalkeeper Ricardo after a poorly-directed defensive header had fallen kindly for him inside the box.

Raul Garcia was almost gifted an equaliser when his shot was fumbled by Sebastian Viera, but the Villarreal stopper got away with it.

Moments later, however, the sides were level when Valdo found himself unmarked and made no mistake from close range.

The home side had a half-chance to go ahead in the 27th minute but Paxti Punal's left-footed volley flew wide.

Alessio Tacchinardi did likewise for Villarreal four minutes later, before teeing up another opportunity for Pires which the former Arsenal man managed to put wide.

David Lopez's corner was then met by Roberto Soldado, who fired wide for Osasuna in the last goalmouth incident of the first half.

Lopez forced a decent save from the fists of Viera two minutes after the restart from a free-kick, and then set up Soldado for a 20-yard shot which the Villarreal keeper did well to hold.

Osasuna continued to push for a second goal with Raul Garcia denied by Viera and Lopez's effort blocked by Gonzalo Rodriguez.

Rodriguez had a shot of his own at the other end in the 63rd minute and, although it was to no avail, the visitors did soon forge into the lead.

The breakthrough came thanks to Forlan, who was not closed down quickly enough and beat his former Manchester United team-mate Ricardo, curling a brilliant shot into the top corner from 25 yards after picking up a pass from Guillermo Franco.

Pierre Webo looked for the instant response for Osasuna but his 20-yarder was too high.

In the 87th minute Villarreal extended their lead through Forlan, who got in behind the Osasuna defence before stabbing an attempted shot goalwards with Ricardo racing out to meet him.

Ricardo managed to get a touch on the ball to slow it up but Forlan was quickest to react and he beat both the keeper and an Osasuna defender in a race for the ball before toe-poking over the line.

Forlan then completed his hat-trick in the third minute of injury time after again breaking clear of the home defence, latching onto a long ball forward and strolling through totally unmarked to slot past Ricardo.

The Osasuna players appeared to have stopped with Carlos Cuellar having fallen to the ground clutching his face after challenging for the ball on the halfway line before Forlan broke through.

The goal stood though, and the victory moves Villarreal to within four points of a UEFA Cup berth with four games remaining.