The home side threatened as early as the first minute when Oriol Romeu threaded a through-ball for Juan Mata but defender James Collins did well to block his goalbound shot for an early Chelsea corner.
The visitors also had their moments in the opening stages of the match mainly through Gabriel Agbonlahor who was using his pace to get the better of the Chelsea defenders, but failed to threaten Petr Cech’s goal.
The opening goal arrived in the 22nd minute when Didier Drogba was brought down inside the box by a clumsy tackle from Richard Dunne.
The Ivorian stepped up to take the resulting penalty kick and although goalkeeper Bradley Guzan got a touch on the ball he was unable to prevent Drogba from scoring his 150th goal for Chelsea.
The goal brought more energy into the match but it was the Villans who held most of the possession and they were soon rewarded with an equalizer five minutes later.
Stephen Ireland stated the move as he found Charles N’Zogbia on the left, who then played the ball back to the Irish player; although his initial attempt looked to have struck John Terry’s arm on the goalline, it didn’t matter in the end as he fired home from the rebound.
The Blues came close to restoring their advantage in the 34th following a good run from Drogba on the left; his cross-cum-shot was parried away by Guzan and the ball fell kindly for Mata, but Stephen Warnock put his body on the line and blocked his attempt, leaving the sides deadlocked at the break.
Alex McLeish’s men should have taken the lead in the 52nd minutein a counter-attacking move which saw Mark Albrighton putting Agbonlahor through on goal, but somehow he failed to pick his spot and allowed Petr Cech to pull off a one-handed save to his left.
Andre Villas-Boas introduced Fernando Torres in the place of Daniel Sturridge in the 62nd minute and he almost made an immediate impact as he rattled the crossbar with a powerful shot a minute later.
The goal almost came from an unlikely source in the 76th minute when another substitute, defender Jose Bosingwa, unleashed a dipping left-footed shot, but Guzan made a great diving save to his left to push the ball over the bar.
Chelsea were made to rue their missed chances in the 83rd minute when Ciaran Clark ran through the Chelsea defenders on the left before playing the ball into the path of Stilian Petrov, who beat Cech with a low left-footed strike towards the far post.
Villa crushed Chelsea’s comeback hopes just three minutes later when Ireland intercepted a Frank Lampard pass just over the halfway line; with no defenders in front of him he had enough composure to lay the ball across for Darren Bent to fire into the back of the net.
Chelsea have now failed to win in their last four matches, drawing three and losing one, and have now dropped to 5th place on the table.