Two Craig Dawson headers either side of Hal Robson-Kanu pouncing on Ospina spilling a cross, and Hector Bellerin failing to clear, were too much for the visitors. Alexis Sanchez's early equaliser proved a mere consolation come full-time.
As Arsenal fans battled out over Arsene Wenger’s future with aerial protests the Gunners found themselves utterly outclassed by a powerful, organised Albion side.
The result heaps further pressure on Wenger, who has yet to decide on whether to sign a two-year contract extension. On the evidence of today’s display Arsenal are going nowhere under his leadership.
Mesut Ozil’s thigh injury prompted a major reshuffle in Arsenal’s frontline, with Alexis Sanchez, Theo Walcott and Danny Welbeck making up the attacking trident for the first time this season. Supported by the energetic Aaron Ramsey and Alex Oxlade-Chamberlain, the visitors began the game full of vim and endeavour.
Yet few watching eyes were on Arsenal’s bright start as the first aircraft hovered into view of the television cameras, trailing with it a demand for “No New Contract” and the immortal hashtag WengerOut.
It wasn’t the only aerial battle Arsenal were losing as West Brom’s set piece superiority paid dividends after 13 minutes. Petr Cech had saved smartly from James McClean but in doing so had handed the Baggies their most formidable attacking weapon.
Ex-Spurs forward Nacer Chadli put the corner in the right area, too far away from an outrushing Cech to reach for a punch, and Dawson had the run on his opponents to slam a header home.
Arsenal were not behind for long as Granit Xhaka grew in influence. He was in far too much space 25 yards out but rather than careen a shot at goal he spotted an unmarked Sanchez, who smashed an effort in via the underside of the crossbar.
As the Chilean was bringing the Gunners level the counter protest was mobilising, with an “In Arsene We Trust” banner soon circling over the Hawthorns.
It took a high-quality game to distract from the Battle of Birmingham in the skies but that is just what these two sides provided. West Brom in particular did not look like a side settling for 40 points. Both Darren Fletcher and Salomon Rondon had joy bursting in behind Nacho Monreal only to drag shots wide.
In the tackle Albion were no less vigorous and James McClean should perhaps have seen more than yellow for a wild tackle on Sanchez that left the goalscorer among the walking wounded.
He wasn’t the only one, with Petr Cech forced to make way for David Ospina after straining a muscle chasing a ball on the edge of the box.
Sanchez returned for the second period with his customary thunderous expression and his frustration showed little sign of easing as West Brom continued their aerial bombardment, Rondon heading just wide from close range.
It made it all the more inexplicable then when Tony Pulis withdraw Rondon for Hal Robson-Kanu, surely not the man to exploit Arsenal’s frailities? Unless the chances are handed to him on a silver platter as Ospina spilled a chip from Chadli into his path.
As the ball rolled through James McClean’s legs Wenger was on his way to remonstrate with the fourth official. He knew how much damage his reserve goalkeeper had wrought on his side’s ambitions for the season.
For all their manager’s talk of “character” in the early months of the season Arsenal spent the next 10 minutes hiding in their shells, a Danny Welbeck header against the crossbar merely inspiring Albion to reassert their superiority. Robson-Kanu outran Koscielny only to see his shot blocked by Ospina, who was lucky Chadli couldn’t take advantage from the rebound.
As Pulis’ men outclassed his Wenger responded by going direct, bringing on Olivier Giroud in a move to give Arsenal aerial superiority. Still though, they could not stop West Brom from corners as Dawson doubled the Baggies’ lead on 75 minutes.
Wenger responded by bringing on Alex Iwobi for Sanchez but there was nothing that could be done to stop Arsenal ceding one of their games in hand in the race for the Champions League. Having played one game fewer they are five points off Liverpool.
As Sanchez made way Arsenal fans chanted “you don’t know what you’re doing” at Wenger. It is increasingly difficult to question that assessment.