Sam Allardyce finally suffered the sinking feeling of relegation from the Premier League after Arsenal beat West Brom 3-1 at the Emirates Stadium. (More Football News)
Albion needed a victory in north London on Sunday to keep their slim hopes of avoiding the drop alive, but the Gunners sent them down with three games to play.
Emile Smith Rowe put Arsenal in front with his first Premier League goal and Nicolas Pepe added a stunning second six minutes later.
Matheus Pereira pulled one back midway through the second half, but Willian rubbed salt into Albion's wounds by scoring an elusive first Arsenal goal late on with a brilliant free-kick.
Victory for Arsenal, who are facing a tough task to qualify for European football next season, shattered Allardyce's proud record of having never been relegated from the top flight.
Albion started like a team knowing they were entering the last chance saloon, with Pereira curling just beyond the post before drilling wide for a second time on the break.
A magnificent last-ditch tackle from Darnell Furlong denied the lively Bukayo Saka at the other end, but the England international was the architect for Arsenal's 29th-minute opener.
Willian played Saka in down the left, and the winger's cross was clinically volleyed in by the onrushing Smith Rowe
Things swiftly went from bad to worse for beleaguered Albion – Pepe afforded the space and time down the right to bend a sublime left-footed strike into the far corner.
Pepe continued to torment, delivering a cross which Gabriel Martinelli and Smith Rowe somehow failed to convert but, with Hal Robson-Kanu perhaps fortunate to escape with a booking when he flung an arm at Mohamed Elneny, Pereira gave West Brom a lifeline.
The Brazilian was allowed to surge forward unchallenged before drilling a left-footed effort into the bottom-right corner.
Albion's fate was confirmed in the 90th minute, though, with Willian sending a superb free-kick beyond Sam Johnstone.
What does it mean? Agony for Allardyce, Arsenal finally fire
It was always going to be a big ask for the 66-year-old Allardyce to keep West Brom up after he took charge in December and any slight hopes of producing a great escape are now over.
It remains to be seen whether he will remain in charge for a Championship promotion push and Albion must recover after being relegated from the Premier League for a joint-record fifth time (along with Norwich City) – and an 11th time in total they have dropped out of the top tier.
Meanwhile, Arsenal fans will wish they had provided such a cutting edge in a goalless draw with Villarreal three days earlier. Pressure will remain on Mikel Arteta – who make six changes to his side – despite what was a first home win in seven attempts.
Saka provides the spark
Teenager Saka was a real thorn in West Brom's side, causing all sorts of problems down the left flank. The 19-year-old made two key passes – including the assist for Smith Rowe's opener – and delivered five crosses, giving another demonstration of his outstanding talent as he attempts to force his way into England's Euro 2020 squad.
Diagne anonymous
Mbaye Diagne endured a frustrating evening leading the line for Albion. While Pereira probed throughout, Diagne did not pose a threat and was replaced by Robson-Kanu 11 minutes into the second half.
What's next?
Ninth-placed Arsenal face a London derby at Chelsea on Wednesday, while downed Albion are at home to Liverpool next Sunday.
