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.
9. Solly March - 4
Delayed pulling the trigger in good position early on. Gave ball away in build up to third goal. Should have done better with a header over the bar from close range. Not his day. Replaced by Adingra Photo: Nathan Stirk/Getty Images
10. Kaoru Mitoma - 4
Kept extremely quiet in the first half, with none of his attacking actions working out. Beaten to the ball by Cash for the opening goal. Much more lively after the break. Brought down after dangerous run. Good header across goal. Wasteful shot from tight angle. Booked Photo: Nathan Stirk/Getty Images
11. Danny Welbeck - 3
Offered no threat in the first half. Gave ball away in the middle of the park with unnecessary chop and nearly led to third goal. Shot saved onto the post but would have been offside anyway. Rightly booked for bad foul. Hooked at half-time. Photo: GEOFF CADDICK/AFP via Getty Images
12. Evan Ferguson - 4
Looked sharp in early stages but was anonymous after Villa ran riot. Sacrificed at half time as both strikers made way for Fati and Pedro. Photo: James Gill/Getty Images