West Brom capped an unforgettable week by outclassing Arsenal to secure a first away win in 19 top-flight games. Chris Brunt had a first-half penalty saved, but Peter Odemwingie later fired the opener from Jerome Thomas's centre. Brunt fed Gonzalo Jara for the second, although Manuel Almunia should have saved his shot, and Thomas made it three after some dismal defending. Samir Nasri scored a late double for Arsenal, but it provided little consolation for boss Arsene Wenger. It was West Brom's second major scalp in the space of four days following Wednesday night's Carling Cup victory over Manchester City, but that was a game contested by what effectively amounted to two reserve sides. This could hardly have been more different, a promoted Albion side producing a performance full of enterprise and endeavour to secure a famous win against a Premier League heavyweight. True, the absence of a clutch of injured stars - including captain Cesc Fabregas and Theo Walcott - meant the home side, who remain second in the league table, lacked their usual creativity and fluency. But Arsenal, their performance as sloppy and error-strewn as West Brom's was inspired and purposeful, looked a long way from being title contenders. Sunderland had delivered an object lesson in how to contain Arsenal last weekend, pressing and harrying to deny the Gunners space and time, but only in the final throes of the game were West Brom forced to settle into a similar pattern. If anything, until Nasri led a belated Arsenal fightback, it was West Brom who looked more credible title aspirants, although they first had to overcome a difficult start. Perhaps betraying understandable unease at the prospect of facing an Arsenal attack that had previously been in electric form at home, scoring 16 goals in three games in all competitions, the Albion defence made a hash of a routine early clearance. A series of attempts to usher the ball away ricocheted around the box, a skewed skyward punt followed, and the danger was finally snuffed out only when Jonas Olsson hacked down Emmanuel Eboue, earning a yellow card. West Brom were soon in trouble again as Eboue swung in a cross from the right and Andrey Arshavin, nipping in ahead of Brunt, side-footed against the post. Briefly, Arsenal threatened to click into gear as Marouane Chamakh headed a Sagna cross wide before Nasri drove a low 25-yard effort just the wrong side of Scott Carson's left-hand upright. But it proved a false dawn for Arsenal, and as West Brom began to press and close down their vaunted opponents, the home side looked increasingly discomfited. Arsenal should have fallen behind when Almunia raced off his line before bringing down Odemwingie on the edge of the area. It was a poor challenge and the Premier League's youngest referee, Michael Oliver, who had a quietly impressive afternoon, rightly pointed to the spot. Brunt's penalty, struck low to Almunia's right, was weak, and the Arsenal keeper redeemed himself by getting down quickly to smother the danger. The Spaniard apparently injured his shoulder in the initial challenge and received treatment at the break, but questions will inevitably be raised about his second-half performance. There was little Almunia could do when Thomas, cutting in from the left, wriggled past Sagna to provide Odemwingie with an easy finish. But he was clearly at fault for West Brom's second, scored by Jara after he had danced through the Arsenal defence. The Spaniard fumbled with the Chile international's shot, which went in off his arms as he crouched to gather the ball. Almunia was equally at fault for the visitors' third, inexplicably racing out to meet Brunt's run into the right-hand side of the area, a manoeuvre which left the Baggies midfielder with the simple task of squaring for Thomas, who gleefully slotted home. Three down in their own backyard, a rocked Arsenal finally stirred. Nasri led the rearguard action, shuddering the bar from range before lashing in his third and fourth goals of the week following his Carling Cup exploits against Tottenham. But West Brom, inspired by the obduracy of a defence brilliantly marshalled by Olsson, hung on for a memorable victory which will inevitably raise questions about Arsenal's title credentials ahead of next Sunday's trip to Chelsea. Arsenal manager Arsene Wenger: "It was a poor performance, defensively and offensively. Not one player performed to their level. "We had an off day and were not good enough to win the game. "We didn't give up, that was the one positive, but we started the game too late and we have to learn from that." West Brom manager Roberto Di Matteo: "I would say we deserved it, the way we played, the way we created chances, scored goals and played very well. "We pressed them very high, we pressed them all over the pitch. We managed not to let them play their usual way. "And when we had the ball we passed it very well and created chances ourselves. Credit: BBC