Swansea City have ended Chelsea's 15-match Premier League unbeaten streak with a 1-0 victory at the Liberty Stadium, reaching the 40-point mark in the process.
Gylfi Sigurdsson scored his ninth league goal since the turn of the year to condemn the Blues to their first defeat under Guus Hiddink and all but secure Swansea's Premier League status for another season.
The visitors were playing in their first match since it was confirmed that Antonio Conte will take over at the club after Euro 2016, and they created the first shooting opportunity of the afternoon too when Ruben Loftus-Cheek fired a crisp strike straight at Lukasz Fabianski.
Asmir Begovic, chosen ahead of Thibaut Courtois for the match, was called into a smart low stop at his near post when Jefferson Montero's deflected cross almost snuck in, before Oscar and Loftus-Cheek both threatened for Chelsea at the other end.
Swansea's first real chances of the contest arrived shortly afterwards as first Sigurdsson was kept out by Begovic before Angel Rangel skewed an effort well off target from inside the area moments later.
Alexandre Pato, making his first start for Chelsea, then failed to hit the target having been picked out by Oscar at the back post, and just two minutes later the visitors found themselves behind.
Montero had been Swansea's danger man all game, and it was the winger who provided a cross into the middle which Matt Miazga could only clear as far as Sigurdsson, who fired a first-time volley past a helpless Begovic.
The hosts should have doubled their lead 10 minutes later too, with Leroy Fer picking up a loose ball at the back post after a corner had been flicked on to him, but he looked for a pass instead of going for goal himself and the chance went begging.
Chances continued to fall to Swansea, although Chelsea weren't helping themselves and a mix-up between Begovic and Baba Rahman gifted Andre Ayew another opening, but the fit-again forward failed to make the most of it.
Fer then couldn't get enough power on a header from Neil Taylor's cross as the Swans pushed on for a second, but they were almost caught out right at the end of the half when Oscar beat the offside trap and the ball eventually fell to Pato, only for the striker to snatch at the chance and slice it wide.
Chelsea made a brighter start to the second half, but the first chance fell to the home side when Montero and Sigurdsson combined to set up Alberto Paloschi, only for a loose touch from the striker to allow Begovic to come out and smother the ball.
The visitors went straight up the other end and created a chance of their own through Pato, whose flick from Pedro's low delivery bounced narrowly wide of the far post.
Begovic was called upon again shortly before the hour mark when Montero's cross was only cleared as far as Jack Cork, who fired a 25-yard volley bouncing into the ground that the keeper was at full stretch to push away.
Swansea should have wrapped the game up with a little under 15 minutes remaining when Sigurdsson skipped past his marker before beating Begovic to the ball and clipping a cross into the middle, but Montero could not keep his header down with the goal gaping.
Chelsea continued to see the vast majority of the ball, but they struggled to find a way past the Swansea defence and Ashley Williams was once again there to thwart Radamel Falcao late on, getting a touch to the Colombian's effort to make it easier for Fabianski.
The home goalkeeper was not tested anywhere near as much as Hiddink would have liked, however, and the hosts were able to comfortably hold on for their first ever Premier League victory over Chelsea to move 13 points clear of the relegation zone.
