Crystal Palace checked Chelsea's progress towards the Premier League title on Saturday, goals from Wilfried Zaha and Christian Benteke earning them a shock 2-1 win over their London rivals.
Cesc Fabregas opened the scoring for Chelsea, who had not lost at home since September, tapping in from an Eden Hazard cross in the fifth minute.
But speedy Palace, who had won their previous three games to climb away from the relegation zone, hit back with two in two minutes, Zaha angling a shot through Chelsea's defence to equalise and feeding Benteke who chipped home.
Palace keeper Wayne Hennessey made a series of fine saves behind a well-organised defence to deny waves of attacking moves from the league leaders.
The defeat allowed second-placed Tottenham Hotspur to move to within seven points of Chelsea with nine games remaining.
Yet despite overseeing perhaps the biggest shock of the Premier League season, Sam Allardyce, who has breathed new energy into struggling Palace, was still left tipping Chelsea to regain the title they last won in 2015.
"It's a sweet three points to come to the champions -- or who I think are going to be champions -- and win," Allardyce told the BBC.
"This is what the Premier League is about. There can be a shock anywhere. It will make people sit up and say 'Wow!'
"I think our performance is typical of what seems to be the character of the side. The defence was outstanding, the goalkeeper was outstanding, the game plan worked exceptionally well."
Hennessey made 11 saves altogether as Palace, who only intermittently lifted Chelsea's siege, had to overcome major defensive setbacks.
Scott Dann, who was brought on at halftime for James Tomkins, had to be taken off on a stretcher just 15 minutes later when he suffered what appeared to be a serious knee injury.
He was given lengthy treatment on the pitch before being carried off. It led to seven minutes of injury time being added -- but Chelsea still could not manage to find a way through.
Manager Antonio Conte said the result proved the title was not yet won. "I always said the league only finishes when you have the mathematics you want. Otherwise, you must fight and play every game to win because in England an easy game does not exist," he told reporters.
"Today we deserved at least to draw because we had many chances to score and we dominated the game."
(Reporting by Clare Lovell and Ian Chadband, editing by Ed Osmond, Neville Dalton)