Two goals from Michael Owen ensured a 2-0 for Newcastle United over Sunderland in the Tyne-Wear derby, while Manchester City beat Portsmouth 3-1 at Eastlands in a match that saw Hermann Hreidarsson sent off late in the first half.
Cast into the bottom three by Bolton Wanderers' victory at Middlesbrough on Saturday, Birmingham's problems were made a whole lot worse as Ashley Young and John Carew helped themselves to two goals apiece.
Young put Villa ahead after 28 minutes, lashing in from the edge of the box from Olof Mellburg's mishit pass.
Then Carew added a second, heading in Young's free-kick just before half-time.
It got worse for Alec McLeish's side eight minutes after the break as Carew notched his twelfth of the season after Gareth Barry - supposedly a target for Liverpool - had surged by the former Villa defender Liam Ridgewell.
Young then got his second, weaving through two half-challenges as he cut in from the left before finishing at the second attempt.
Mikael Forssell did pull one back from James McFadden's pass midway through the second half, but Gabriel Agbonlahor capitalised on a weak Ridgewell clearance to restore the four-goal margin.
With three games of the season remaining, the defeat leaves Birmingham a point behind Reading and Bolton, and a further three adrift of Sunderland, Middlesbrough and Wigan Athletic.
"It's all about our next three games - we have to take as many points from those games as we can. This match doesn't mean we're going down," McLeish said.
"We were on the end of a bruising from a really good Villa side. Villa's front men were on fire and we were unable to string any passes together until the second half.
"You have to say that Villa's agenda is totally different to ours - the bottom line is that they are a better team."
"I can take some things from the game and we have been a different team at home."
Sunderland could have pulled further clear, but they were well- beaten by Newcastle United, with Owen scoring both goals in a 2-0 win.
Without the injured Jonny Evans and Phil Bardsley, Sunderland never looked comfortable at the back.
They fell behind after four minutes as Owen got in front of Paul McShane to head in Geremi's cross, and then suffered a killer blow just before half-time as Owen converted from the penalty spot after Danny Higginbotham had handled.
The former Liverpool striker has now scored six goals in his last six games, as Newcastle have eased away from relegation danger.
Sunderland improved after the break, and although Kenwyne Jones went close with a header never looked like getting back into the game.
City are now just two points behind Portsmouth in seventh after their 3-1 win over Harry Redknapp's side.
Darius Vassell gave City an early lead after a mistake from David James and Martin Petrov doubled the advantage with a deflected strike.
John Utaka pulled one back for Portsmouth but Hreidarsson was sent off for a foul on Vassell just before half-time.
Portsmouth actually took the game to City in the second half with just 10 men but Benjani sealed the points against his former side with City's third after a neat turn and powerful shot.
By Ben James, dpa