But Arsene Wenger's side will be happy to take a slender lead to El Madrigal next Tuesday, and happy too to have kept another clean sheet - their ninth in a row - and so prevented Villarreal getting a vital away goal.

Arsenal ended 40 minutes of first-half frustration before beaking the deadlock through Kolo Toure, who from six yards reached out and poked home a low, hard cross from Aleksander Hleb. But Villarreal should have had a penalty minutes later when a clumsy challenge by Gilberto just inside the area brought down Jose Mari.

The Yellow Submarine frustrated Arsenal with their well-disciplined back-four and three-man midfield holding a high line and forcing Arsenal into the congested centre where the visitors repeatedly broke up the Gunners' attacks.

In the first half, Arsenal's most potent attacking threat repeatedly came down the left and involved Flamini, Ljungberg or Henry.

The Gunners thought they'd taken the lead after 12 minutes when Gilberto fed Fabregas, whose astute pass was finished in typical style by Henry. But the Frenchman was adjudged to be marginally offside. The decision was shown by TV cameras to have been wrong.

The only goal came after an Henry corner was headed back out to him. He found Hleb who had lost his marker Senna and hit a low, hard cross into the six-yard box where Toure stabbed it home.

Eboue and Hleb gave Arsenal more width down the right flank after the break, and Arsenal enjoyed a strong opening 20 minutes to the second-half. But Villarreal continued to close down the Arsenal attacks, and it was half-chances rather than genuine opportunities that came the Gunners' way.

Gilberto, Henry and Bergkamp were all thwarted as Arsenal sought the second goal that would have gien them more breathing space.

So the tie remains nicely poised. Villarreal were by no means overawed, and Riquelme showed his class in flashes in a hard-working display.