A debut goal from Zat Knight and a late Gabriel Agbonlahor strike saw Aston Villa end Chelsea's 18-match unbeaten streak in the league.
Zat Knight made it a dream debut for Villa
Knight climbed above Didier Drogba to head in a Gareth Barry corner in the second minute of the second half.
Chelsea threw everything at Villa in the final half hour but came up against a determined Villa backline.
Salomon Kalou dragged a shot wide before Villa broke and Agbonlahor stabbed in Ashley Young's driven cross.
It was a frustrating afternoon for Jose Mourinho at Villa Park, where Chelsea have not won in the league since 1999.
But it was a terrific game for the neutral - not to mention the Villa fans - with an Agbonlahor shot on the turn that was beaten out by Petr Cech firing an early warning sign that Martin O'Neill's side meant business.
Chelsea went close through long-range efforts by Michael Essien and Florent Malouda.
John Terry headed over and Shaun Wright-Phillips saw a shot well turned around the post by Scott Carson as Chelsea began to move up the gears.
It was real end-to-end stuff with the quartet of Young, Agbonlahor, John Carew and Luke Moore providing a new-look Chelsea backline with plenty to think about.
Drogba was not enjoying his most profitable afternoon as Villa's own reworked defence made him fight for everything.
He showed great strength to hold off Martin Laursen, but having done the physical work he could not add the finishing touch and shot wide from the edge of the area.
A lively Wright-Phillips lashed into the side-netting but there was a let-off for Chelsea just before half-time when a Young cross fell for Barry, only for Moore to get in his way attempting an ambitious overhead kick.
Villa have yet to score a league goal in the first half this season, but whatever manager O'Neill says at half-time seems to be working.
Within a minute of the kick off Young had a shot tipped over by Cech and from Barry's corner Knight climbed above Drogba to head powerfully past Cech.
The home side made it hard for Chelsea at Villa Park
It was the second goal in successive games for £3.5m capture Knight - the other an own goal for Fulham on his last visit to Villa Park that also helped provide his new employers with the three points.
Mourinho wasted no time in throwing Claudio Pizarro on, soon to be followed by Joe Cole and Kalou.
But despite plenty of possession and some nervous moments for the home side, Chelsea struggled to come up with clear-cut chances.
Their best opportunity to equalise looked to be from a set-piece, with Terry heading over from one of their succession of corners.
Kalou shot wide from a promising position but as Chelsea poured forward they left themselves open to Villa's pace, and when Young broke down the left his driven effort was guided in by Agbonlahor.
Aston Villa manager Martin O'Neill:
"It's a great day. Chelsea are brilliant and we're delighted that we've won.
"Zat's goal calmed us down then Chelsea took the initiative slightly, but we kept at it and grabbed a second.
"I was very, very pleased with their attitude. It has been terrific since the opening day defeat to Liverpool and this will give us a big, big boost."
Chelsea manager Jose Mourinho:
"It was a good game with good teams but a result that Chelsea didn't deserve at all.
"We dominated the first half, reacted well to their goal and we deserved to get a point at least.
"We made a mistake at the corner for their goal. We shouldn't be conceding goals like that but also had enough chances to score."
Aston Villa: Carson, Mellberg, Knight, Laursen, Bouma, Agbonlahor, Reo-Coker, Barry, Young, Moore, Carew (Petrov 79).
Subs Not Used: Taylor, Harewood, Gardner, Maloney.
Booked: Reo-Coker, Barry, Agbonlahor, Carew.
Goals: Knight 47, Agbonlahor 88.
Chelsea: Cech, Belletti, Terry, Alex, Ashley Cole, Wright-Phillips (Joe Cole 63), Makelele (Kalou 63), Essien, Malouda, Obi (Pizarro 52), Drogba.
Subs Not Used: Cudicini, Ben-Haim.
Ref: Mark Clattenburg (Tyne & Wear).