Match ends, Crystal Palace 1, Chelsea 0.
Chelsea's title challenge suffered a setback as Crystal Palace boosted their Premier League survival hopes with a richly deserved win.
In a pulsating game, Palace played at a quicker tempo, displayed the greater quality and could easily have won by a bigger margin - John Terry's own goal from Joel Ward's teasing cross settling matters.
Even a point would have been a significant blow to a Blues side who remain top, one point clear of Liverpool and two clear of Manchester City, although Manuel Pellegrini's team have played two matches fewer than Chelsea.
The Eagles, playing in front of a sold-out and deafeningly loud Selhurst Park crowd, are now five points clear of the relegation zone after Cardiff's 3-3 draw with West Brom.
Chelsea can have no complaints after a performance lacking urgency and organisation, and characterised by misplaced passes from the off. It was in stark contrast to the display that blew away Arsenal in last week's London derby.
Fernando Torres did have an early close-range strike blocked and had a half-hearted appeal for a penalty turned down.
And Chelsea almost took the lead when a superb break on the left flank saw Cesar Azpilicueta's cross turned behind by a combination of Andre Schurrle and Ward.
But Palace were the better side after a relatively quiet opening 20 minutes, defending deep and denying the visitors the space they so expertly exploited against the Gunners.
They were also increasingly threatening in attack, as Yannick Bolasie shot wide, Blues goalkeeper Petr Cech made a couple of good saves and Adrian Mariappa twice nearly set up goals with incisive runs down the left.
The first of these saw the full-back find Bolasie, who failed to set himself in time for the driven cross and made a mess of the follow-up shot.
Eagles boss Tony Pulis was then left flailing his arms in disbelief as his side failed to win a penalty when referee Lee Mason ignored Gary Cahill's clumsy charge into Cameron Jerome.
Pulis's counterpart Jose Mourinho was similarly animated, although his anger and copious note-taking was prompted by a poor, disjointed first-half performance.
The ineffective David Luiz was taken off at the break and replaced by fellow Brazilian Oscar but it did not spark a Chelsea improvement.
Within seven minutes of the restart, the Eagles deservedly led when, under pressure from Joe Ledley, Terry headed Ward's left-wing cross into his own net.
Eden Hazard almost levelled within a couple of minutes with a curled effort that was superbly tipped wide by home goalkeeper Julian Speroni.
It was the signal for a final half-hour full of chances at either end.
Terry nearly made amends for his mistake with a header from a corner that went just over, while Frank Lampard was denied by Speroni, who brilliantly anticipated the England midfielder's strike.
But it was Palace who continued to pose the greater danger. Jason Puncheon's cross-shot drifted just wide, Jerome's thumping low shot hit the post, Ledley twice dragged efforts wide and Stuart O'Keefe had a shot tipped over.
The second goal ultimately proved unnecessary, although a terrible back-pass by O'Keefe almost gifted a Torres an equaliser before Palace saw out four minutes of injury time to secure the win.
Crystal Palace manager Tony Pulis said:
"It's a very important result for us. Our results had dropped off, but the performances had been OK, but to beat Chelsea will give everyone a boost to push on for the last seven games.
"The Premier League is the most competitive league in the world and that's why it's a great league. The top teams always have to play well or they can come unstuck.
"Chelsea are a fantastic club and it's a great result for us. We picked the team on Monday and just worked through it for four days. We had a few chances in the second half and I'm pleased we got through the game."
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- 3MariappaBooked at 90mins
- 6DannBooked at 77mins
- 13PuncheonBooked at 20minsSubstituted forParrat 90+1'minutes
- 30JeromeSubstituted forMurrayat 88'minutes
- 7BolasieBooked at 13minsSubstituted forO'Keefeat 70'minutes
- 26TerryBooked at 32mins
- 4David LuizSubstituted forOscarat 45'minutes
- 8LampardSubstituted forSalahat 56'minutes
- 14SchürrleSubstituted forBaat 70'minutes
- 17E Hazard
- Lee Mason
- Shots on Target
Second Half ends, Crystal Palace 1, Chelsea 0.
Substitution, Crystal Palace. Jonathan Parr replaces Jason Puncheon.
Adrian Mariappa (Crystal Palace) is shown the yellow card.
Substitution, Crystal Palace. Glenn Murray replaces Cameron Jerome.
Attempt missed. Fernando Torres (Chelsea) right footed shot from the left side of the box is high and wide to the right.
Attempt blocked. Branislav Ivanovic (Chelsea) header from the centre of the box is blocked. Assisted by Oscar with a cross.
Corner, Chelsea. Conceded by Damien Delaney.
Corner, Chelsea. Conceded by Cameron Jerome.
Attempt missed. Joe Ledley (Crystal Palace) right footed shot from the left side of the box misses to the right. Assisted by Cameron Jerome.
Corner, Crystal Palace. Conceded by Petr Cech.
Attempt saved. Stuart O'Keefe (Crystal Palace) right footed shot from outside the box is saved in the top right corner. Assisted by Kagisho Dikgacoi.
Attempt saved. Jason Puncheon (Crystal Palace) right footed shot from the right side of the box is saved in the centre of the goal. Assisted by Kagisho Dikgacoi.
Attempt blocked. Nemanja Matic (Chelsea) left footed shot from outside the box is blocked. Assisted by Mohamed Salah.
César Azpilicueta (Chelsea) wins a free kick in the defensive half.
Foul by Jason Puncheon (Crystal Palace).
Scott Dann (Crystal Palace) is shown the yellow card for a bad foul.
Fernando Torres (Chelsea) wins a free kick on the left wing.
Foul by Scott Dann (Crystal Palace).
Attempt missed. Nemanja Matic (Chelsea) left footed shot from outside the box misses to the right. Assisted by Oscar.