Uruguayan striker Diego Forlan put the visitors ahead only for Adriano, who was unsure of his place in the starting line-up due to an alarming loss of form, to equalise six minutes later.

Nigerian international Obafemi Martins, a first-half substitute for Alvaro Recoba, netted Inter's second goal nine minutes into the second half to complete the turnaround for the two-time European champions.

Villarreal's mercurial Argentine midfielder Juan Roman Riquelme hit the bar in the 63rd minute, but Inter held on for a precious victory.

Competing in the Champions League for the first time, Villarreal will be kicking themselves for throwing away their early advantage, but their away goal means they are still very much in the tie.

The second leg takes place next Tuesday and the winners will meet either Juventus or Arsenal in the semifinals.

Inter coach Roberto Mancini was proud of his team for recovering from their early setback.

"We paid for a lapse in concentration and it could have been disastrous," he said.

"But the players deserve a lot of credit for the way they came back immediately.

"With a bit more luck we might have scored a third goal, which would have made life a little easier in the second leg.

"But having come back from an extremely difficult situation, I'm more than happy with the result."

Mancini opted to play Recoba up front alongside Adriano, while Cesar replaced the injured Luis Figo in midfield.

Villarreal were decimated by suspensions with Alessio Tacchi-nardi, who moved to Spain last summer after 11 years with Italian giants Juventus, Josico and Rodolfo Arruabarrena all ruled out.

Inter were caught cold with just 45 seconds on the clock.

Jose Mari burst in between Pierre Wome and Walter Samuel and his low shot was palmed away by Francesco Toldo.

The loose ball ran kindly for Forlan, who tucked home his second goal of the competition.

The home side came close to levelling the score 60 seconds later.

Adriano broke the offside trap to race after Dejan Stankovic's chipped pass, before lobbing the ball over Villarreal keeper Sebastian Viera.

Javi Venta sped to reach the Brazilian's goalbound effort, and managed to hook the ball clear just before it crossed the line.

Adriano cursed his luck, but fortune soon smiled upon him.

The powerfully-built South American had his back to goal when Juan Manuel Pena's attempted clearance fell at his feet, and with a quick turn he slammed a left-footed shot into the net from six yards.

Recoba tested Viera from distance with a low drive, before limping off with an injury and making way for Martins.

Adriano curled two identical 20-yard free-kicks over the bar and sent a free header inches wide as Inter ended the half in complete control.

The break failed to interrupt Inter's momentum and they took the lead in the 54th minute.

Juan Sebastian Veron fed Stankovic down the right touchline and he flicked the ball over Juan Pablo Sorin's head and went haring towards the box.