Arsène Wenger endured another black day in the Black Country, his side comfortably beaten by a West Bromwich Albion team who, in losing their last two matches, appeared to have switched off on reaching 40 points.

There was no such luck for the visitors, who remain outside the top four after losing for a fourth time in five league games and will not gain their annual pass into the Champions League playing like this. Two of the goals Arsenal conceded were from set pieces, always on the cards against a Tony Pulis side, and the one in between followed a farcical mix-up in defence.

There were occasional flickers of interest from Alexis Sánchez, at least until his mobility was reduced by a wild challenge that brought James McClean a booking, though players such as Theo Walcott and Danny Welbeck were merely peripheral presences. “There’s only one Arsène Wenger,” could be heard throughout the game; unfortunately it was the home fans doing the chanting.

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West Brom got off to a flying start. After breaking into the Arsenal penalty area Allan Nyom might have done better after five minutes than hammer a cross across the face of goal that neither Salomón Rondón nor Darren Fletcher could reach. But when Chris Brunt’s inspired pass allowed McClean to bring an early save from Petr Cech the home side took the lead from the corner. Nacer Chadli’s delivery was excellent andCraig Dawson timed his leap to perfection to climb above Laurent Koscielny and head down and in from barely two yards out.

From that point on it looked as though it might be another long afternoon for Wenger, subjected to the indignity of a light aircraft buzzing the ground trailing a banner demanding his removal, though his players did manage to dust themselves down and draw level within four minutes. Granit Xhaka’s diagonal ball picked out Sánchez unmarked at the far post and before the home cover could close him down he had controlled the ball with his chest and rifled a shot past Ben Foster.

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The action was evenly balanced for the remainder of the first half, so much so in fact that another plane appeared carrying a banner reading: “In Arsène We Trust.” Typical Arsenal. Why stop at one ostentatious gesture if you can afford two?

On the pitch Walcott was unable to convert at one end after Sánchez had won the ball from Chadli, and Fletcher brought a save from Cech at the other with a shot on the turn from Jake Livermore’s neat pass behind the Arsenal back line. That turned out to be the Arsenal goalkeeper’s last significant action, for he pulled up sharply in the act of passing to Xhaka a couple of minutes later and immediately signalled he could not carry on and was replaced by the Colombian David Ospina.

The second half opened with Rondón missing a header in front of goal after reaching Brunt’s cross ahead of Koscielny, at which point Pulis hooked his striker in favour of Hal Robson-Kanu. This looked like a stroke of coaching genius when the substitute scored with his first touch.

There was an element of comedy to the goal, Ospina leaving his line to deal with Chadli’s chip into the box but succeeding only in finding Robson-Kanu. Although Arsenal felt McClean was both offside and interfering he was not actually obstructing anyone by allowing the ball to roll through his legs. “I thought he was offside at first,” Wenger admitted. “I’ve seen replays since and he wasn’t.”

Facebook Twitter Pinterest Another banner flown over the Hawthorns during Arsenal’s defeat. Photograph: Andrew Boyers/Reuters

Olivier Giroud took the field on his usual rescue mission but it was Welbeck who slapped a header against the crossbar from Xhaka’s corner, before Ospina made some amends for his earlier misjudgment by leaving his line promptly to deny Robson-Kanu a second.

Though Wenger could be seen debating the legitimacy of West Brom’s second goal with the fourth official for some minutes afterwards, any sense of grievance Arsenal had went out of the window when the home side scored a third. Again from a corner, again from Dawson, this time finding space for a free header on the six-yard line.

At such times Wenger really must feel like giving up. “You don’t know what you’re doing,” was the travelling support’s reaction to the sight of Sánchez being replaced by Alex Iwobi, even though Wenger felt the Chilean should not have come out for the second half. The home fans were blunter still, with: “You’re getting sacked in the morning.” While it would be an enormous surprise were that actually to happen, Wenger’s team are not currently doing him any favours.