On a day the club celebrated 125 years since their first professional match Albion produced a performance to match the occasion as they stunned the Premier League champions.
Goals from Pascal Gross, Babis Kostoulas and Chema Andres, on his first league start, secured a victory every bit as convincing as the score suggests.
It’s hard to recall a better performance under Fabian Hurzeler who watched on proudly as Albion dominated from start to finish.
In every aspect of the game his side were pretty faultless: pressing, passing, defending and - most importantly - finishing. It was one of those special days at the Amex which will be remembered for a long time by the vast majority of a record crowd of 31,944.
Babis Kostoulas salutes the Amex after making it 2-0. 📷James Boardman
The wonderful pre-match atmosphere clearly lifted Albion who tore into Arsenal from the kick-off.
Ferdi Kadioglu fired over from outside the box and when Albion pressed again and won the ball high up Kostoulas’s volley was heading inside the far post but David Raya’s fingertips diverted it wide.
Arsenal settled into the game and Luka Vuskovic had to make an important interception to dispossess Christos Tzolis when he was put through down the middle.
But it was Albion who broke the deadlock on 31 minutes thanks to the brilliance of Gross.
Chema Andres and Kostoluas were involved in the build-up leaving Gross with a yard of space on the right-hand side of the box. His right-foot shot curled past Reya, struck the near post and went in off the inside of the far upright.
Babis Kostoulas doubles Albion's lead just before the break. 📷James Boardman
Kostoulas found himself in even more space but from 22 yards failed to test Reya - but Albion were in control and went close to a second when Kadioglu’s pull back found Yasin Ayari whose first-time shot from the angle of the six-yard box hit the corner of post and bar.
Bukayo Saka squandered Arsenal’s best first-half chance when he didn’t get enough contact to trouble Bart Verbruggen after Martin Odegaard picked him out in the six-yard box after a breakaway.
Verbruggen threw the ball out to Andres and suddenly space opened up for Kostoulas on the edge of the D. He needed no second invitation, slamming a right-foot shot inside Raya’s right-hand post for 2-0 on the stroke of half-time.
Could Albion find the same level of intensity and discipline in the second half? It didn’t take long before they emphatically answered in the affirmative.
Chema Andres celebrates in front of the North Stand after making it 3-0. 📷James Boardman
Kostoulas had already dragged a shot wide six minutes into the second half when Albion made it 3-0 on 57 minutes. Gross swung over a corner from the left and Raya was nowhere as Andres rose unchallenged and nodded the ball in off the inside of the post.
Verbruggen saved superbly with his legs when Kai Havertz was in on goal to ensure Albion got the clean sheet their defensive display deserved while at the other end they kept looking for more goals. Substitute Matt O'Riley might have had two in the closing stages, but was denied on both occasions by Raya's reflexes.
Albion had to settle for three but it was an afternoon to remember at the Amex.
Albion: Verbruggen, Boscagli, Struijk (Svoboda 86), Vuskovic, De Cuyper, Kadioglu (Costinha 76), Andres (Yalcouye 86), Gomez (O'Riley 33), Ayari, Gross, Kostoulas (Georginio 76).
Subs not used: Steele, Hadjam, David, Osman.
Attendance: 31944