The measure of Villa's outstanding win was a true reflection of their finishing power as they raced in sixth spot and another step closer to European football next season.
Chelsea's surprise defeat opened the door for Manchester United to move closer to the runners-up spot and was due in the main to their indifferent finishing.
The result hardly justified Claudio Ranieri including only three players from the side held to a draw by Middlesbrough on Saturday but there was no dramatic improvement in a game of contrasting fortunes.
The Champions League favourites made a blistering start and threatened to over-run Villa when Hernan Crespo put them ahead after only nine minutes when Adrian Mutu's shot hit the post and bounced back into the path of the Chelsea striker.
Villa, to their credit, held on grimly in this period to produce their best result of the season.
The game, however, effectively changed direction as a result of a 36th minute penalty when Mario Melchiot needlessly fouled Gareth Barry. Vassell converted the spot-kick to immediately raise Villa's hopes.
But Villa's purple patch occurred in a three minute spell at the start of the second half when shell-shocked Chelsea were completely destroyed as a result of some uncharacteristic weak defensive work.
Unlike Chelsea and their star-studded squad Villa are down to the bare bones after releasing 12 players during the season.
But they have surprised a lot of people by enjoying a better than expected season.
This was exemplified with their unlikely success over a Chelsea side which conceded only three goals for the second time this season.
Chelsea, beaten for only the sixth time this term, had no excuse as they were caught cold at the start of the second half.
The Londoners failed to heed the warning when Vassell had a shot parried by Marco Ambrosio when the ball rebounded into the path of Peter Crouch who amazingly shot wide of an open goal.
But this was all forgotten two minutes later when Vassell put a short pass into the path of Hitzlsperger.
Much to the delight of the Villa fans the German hammered in a powerful left-footed low drive past Ambrosio.
Before a shell-shocked Chelsea had any time to recover they found themselves deeper in trouble in the 51st minute.
A throw-in to the near post by Jlloyd Samuel was flicked on by Crouch to Hendrie who swivelled and shot from close range for the third goal.
Ranieri used his three substitutions but Villa were in no mood to allow Chelsea back into the game despite some industrious work by Scott Parker.
But were generally off the pace and never really threatened to pull the game out of the fire with Crespo obtaining his second goal in the last minute of the game.
Aston Villa: Sorensen, De la Cruz, Mellberg, Johnsen, Samuel, Hendrie (Whittingham 55), McCann, Hitzlsperger, Barry, Vassell (Dublin 88), Crouch (Luke Moore 82). Subs not used: Postma, Ridgewell.
Chelsea: Ambrosio, Melchiot (Gallas 61), Terry, Huth, Bridge, Parker, Lampard, Geremi, Duff (Gronkjaer 71), Mutu (Cole 71), Crespo. Subs not used: Gudjohnsen, Sullivan.
Booked: Huth.
Attendance: 41,112.
Referee: J Winter (Cleveland).