Aston Villa have moved above Chelsea and into ninth position in the Premier League table courtesy of a 2-0 victory at Stamford Bridge in Saturday's late start.
Ollie Watkins sent the visitors ahead in the 18th minute of the contest in London before John McGinn doubled their advantage with an excellent strike early in the second period.
Unai Emery's side have now picked up 13 points from their last four league games during an excellent run of form, while it is a first loss for Chelsea since the end of February, with the result leaving them 11 points behind fourth-placed Tottenham Hotspur.
Mateo Kovacic sent one high of the Villa crossbar in the second minute after the ball broke for the Croatian midfielder just outside the away team's penalty box.
Chelsea had an even better opportunity in the sixth minute when Villa goalkeeper Emiliano Martinez put his team in trouble with a poor pass to Boubacar Kamara inside the box, but the World Cup winner then made a brilliant save to deny Mykhaylo Mudryk.
© Reuters
Villa had a chance of their own down the other end less than a minute later, but Watkins dragged his attempt wide after being given all sorts of space.
Emery's side came close once again in the 17th minute when a brilliant move ended with McGinn striking towards the top corner, but the crossbar came to Chelsea's rescue.
Villa did manage to take the lead in the 18th minute, though, and it was an excellent finish from Watkins, who raced onto a pass from Douglas Luiz before lifting the ball over the onrushing Kepa Arrizabalaga.
Chelsea looked for an immediate response through Joao Felix, who attempted to pick out the corner with a powerful strike, but Martinez was on hand to make a smart save, before Enzo Fernandez headed just wide of the post in the 23rd minute.
Martinez then kept out Kai Havertz's strike in the 25th minute, but Villa remained so dangerous on the break, with Jacob Ramsey's pace causing all sorts of problems.
© Reuters
Mudryk should have levelled the scores in the 31st minute when he was played through by Kovacic, but the Ukraine international could only place his effort into the body of Martinez, before Ben Chilwell struck the outside of the post from close range 10 minutes before the end of the first period.
Felix then had one deflected wide following a period of pinball inside the Villa box, before Martinez did well to deny Havertz, as the Blues continued to press.
Chelsea thought that they had levelled in the closing stages of the first half through a header from Chilwell, but the goal was disallowed, with the defender pushing Ashley Young before making contact with the cross.
Marc Cucurella struck one high of the Villa crossbar early in the second period, with Graham Potter's side making the faster start to the half.
However, the game's second goal came for Villa in the 56th minute, with McGinn finding the corner of the net with a brilliant effort from the edge of the penalty box, with the ball curling away from Kepa.
© Reuters
Kalidou Koulibaly headed over the away side's crossbar on the hour, before Chelsea had a shout for a penalty when Tyrone Mings appeared to handle inside the box, but VAR agreed with the referee that the play should continue, much to the frustration of Felix, who was the closest Chelsea player to the incident.
The returning N'Golo Kante missed the target with a low strike in the 65th minute, and Villa continued to defend impressively, with the score staying 2-0 heading towards the final 10 minutes.
Leon Bailey swung one just wide of the Chelsea goal in the 81st minute, and there was no serious late response from the hosts, who dominated the ball but lost the contest at Stamford Bridge.
Chelsea will be bidding to return to winning ways when they host Liverpool on Tuesday, while Villa will aim to continue their excellent run when they head to Leicester City on the same night.
Matt Law
