Jordan Clark's goal was not enough to prevent relegation
Luton Town suffered a second successive relegation and will play in League One next season after slumping to defeat at West Bromwich Albion.
The Hatters needed a win to guarantee their Championship survival but were instead well beaten at the Hawthorns to fall into the third tier, only a year after they dropped out of the Premier League.
Tom Fellows and Callum Styles both scored twice for Albion along with a header from injury-hit striker Daryl Dike, rendering Millenic Alli's double and Jordan Clark's strike for Luton irrelevant.
And with Portsmouth unable to bail Matt Bloomfield's side out by beating Hull City, it was Luton who tumbled into League One due to an inferior goal difference after they and the Tigers both finished on 49 points.
Luton looked doomed in mid-April but three successive wins - a timely, season's best run of Championship form - lifted them from second bottom to one place outside the relegation zone, putting their fate in their own hands heading into the final day.
They began confidently but their positive start was punctured when Fellows squeezed a shot past Luton goalkeeper Thomas Kaminski just seven minutes in.
That plunged Luton into the bottom three but their response was almost instantly to climb back out of it again.
Thelo Aasgaard regained possession in midfield and released Alli, who tricked his way past Kyle Bartley before firing Luton's equaliser into the far corner.
But the visitors' afternoon, and defence, quickly and disastrously fell apart.
Firstly, Hull went ahead at Portsmouth to plunge the Hatters back into the drop zone.
Then, a header from Dike on the half-hour - his first league goal since March 2023 on his first league start since April 2023 - followed by Fellows' second goal just three minutes later, left Luton with a mountain to climb.
Millenic Alli (right) scored twice at West Brom but Luton still fell to a 5-3 defeat
Luton's situation was desperate and Bloomfield took the drastic step of making a double substitution, which included withdrawing captain Carlton Morris and changing formation at half-time.
It made little initial difference though Luton were boosted when news of a Portsmouth equaliser filtered through.
But two Styles goals in four minutes left Bloomfield's men needing Portsmouth to complete their comeback and beat Hull at Fratton Park.
Clark curled in a second Luton goal just four minutes later before Albion's Isaac Price almost scored a bizarre own goal and Alli did make it 5-3 with two minutes to go, as there were more goals scored in West Brom's final game of the season than the seven scored in their first eight games.
But, from Luton's perspective, their fightback was too little, too late and they will be back in League One for the first time since 2018-19.
'Sorry to our supporters' - reaction
West Brom interim manager James Morrison told BBC WM:
"We haven't been able to put the ball in the back of the net all season and then five come at once. I'm disappointed with the goals [we conceded] but overall I'll be happy with the attacking threat. That was the most entertaining bit.
"I totally understand that [fans asking where that performance was all season] and I'll be asking myself that question.
"Every time we went forward we looked like we were going to score. Lots of frustration from the season but, today, I'll take lots of pleasure from that."
Luton Town manager Matt Bloomfield told BBC Three Counties Radio:
"It is a particularly painful moment for us and everyone associated with our football club.
"Really disappointing performance considering the day and the performance that we needed to get ourselves out of where we were.
"Sorry to our supporters travelling up and down the country, supporting us this season. We understand their disappointment and anger right now."
Matt Bloomfield was unable to save Luton following his mid-season appointment
Revival came just too late for Hatters
It took Luton Town, who played in the top flight of English football for several seasons in the 1980s and early 1990s before a prolonged period of decline, 10 years to climb back from the National League to the Premier League.
There were unforgettable scenes after Rob Edwards' side beat Coventry City on penalties at Wembley in the 2023 play-off final.
But the great adventure lasted only one season and now they are facing life back in League One following back-to-back relegations.
Last summer, Edwards expressed the hope that he had a squad capable of challenging at the top end of the table, but a series of injuries, especially in defence, and a dismal away record undermined his ambition.
He was sacked in January after a run of four successive defeats, leading to the instalment of Bloomfield, plucked from a third-tier promotion challenge with Wycombe Wanderers, as his replacement.
A 1-1 draw at Sheffield Wednesday finally ended a run of 11 away defeats in a row but it took time for Bloomfield to steady the ship, failing to win any of his first eight games in charge despite the addition of new faces, some like Thelo Aasgaard and Millennic Alli from his old League One 'stamping ground'.
Victory over Portsmouth on 1 March finally got things moving in the right direction and back-to-back-to-back wins over Derby County, Bristol City and Coventry finally lifted them out of the bottom three with one game to go.
They came up short on the final day, but with plans approved for a brand new 25,000 seater stadium, which may be ready to stage matches in 2028, the Hatters will rely on Bloomfield's League One knowhow to reverse their fortunes and start them moving in an upwards direction once again next season.
