Ollie Watkins netted a hat-trick as Albion suffered their third loss in four games in all competitions.
Looking to bounce back from the 1-0 Carabao Cup defeat at Chelsea, Roberto De Zerbi made nine changes.
However, they never really got going and found themselves a goal down after just 14 minutes when Watkins scored from Matty Cash’s cut-back.
The striker scored again seven minutes later, with a fine solo effort, after the Seagulls gave the ball away cheaply in midfield. However, Jason Steele appeared to have his vision impeded by Nicolo Zaniolo, who was standing directly in front of him in an offside position. VAR checked but ruled in favour of Villa.
Things went from bad to worse when a hapless Pervis Estupinan turned the ball into his own net after Moussa Diaby's mis-hit was going wide. There was controversy again as Solly March looked like he was fouled in the build-up.
There were shades of Everton's win at the Amex last season as Villa looked like scoring every time they went forward against an all at sea Albion side, lacking protection in front of the defence.
De Zerbi made three half-time changes, with Ansu Fati and Joao Pedro replacing the ineffective Evan Ferguson and Danny Welbeck. Estupinan also made way for Tariq Lamptey.
The substitutes made an immediate impact with Pedro battling hard to keep the ball alive before Fati tapped in from close range on the 50th minute. The goal was given after a lengthy VAR check for offside.
Suddenly, Albion looked more lively in the forward areas but there efforts to find two more goals left them even more open at the back. Watkins took full advantage by sealing his hat-trick to put the result beyond doubt.
Tensions threatened to boil over as Fati lashed out after a tussle with Ezri Konsa but he fortunately escaped with a yellow card.
Jacob Ramsey added a fifth for Villa with a delightful finish off the post to send Albion fans heading for the exit door.
Douglas Luiz added the cherry on top of the cake with a sixth goal in injury-time after Steele had saved well from Watkins.
Here’s how we rated Brighton’s players on a difficult afternoon in Birmingham.
5. Lewis Dunk - 3
Out of sorts. Bad start when he ran ball out of play needlessly. Unable to assert control over defence which was all at sea in the first half. A couple of good blocks. Booked Photo: James Gill/Getty Images
6. Pervis Estupinan - 2:
Taken off at half-time after horror first half. Turned the ball into his own net when a shot was going way wide. Careless fouls and heavy touches. Everything seemed to be going wrong for the full-back. Photo: James Gill/Getty Images
7. Jack Hinshelwood - 4
A baptism of fire in his first Premier League start. Didn’t too much wrong on the ball but offered little protection in front of the defenders. Penalised for foul as Albion progressed into the box. Important interceptions and a nice backheel to Fati but he was overpowered in midfield again as Villa sealed the game Photo: Nathan Stirk/Getty Images
8. Billy Gilmour - 5
Started the game really well with some lovely passing. Soon overpowered as Villa took control of the midfield. Sloppy passes crept into his game and gave the ball away in the build up to the fourth goal Photo: Nathan Stirk/Getty Images