Crystal Palace equalised late to leave Chelsea winless in four Premier League games - and looking over their shoulder in the race for a Champions League slot - as Jean-Philippe Mateta cancelled out Cole Palmer's first-half opener.
Chelsea had chances to seal victory before Mateta picked up a ball from Eberechi Eze in the 82nd minute and blasted home from close range to ease Palace's relegation worries.
Palmer had given the visitors a deserved lead in the 14th minute when he fired in an angled shot after fine work on the left by winger Jadon Sancho who dummied his marker on the halfway line to sprint free and set up the England forward.
The draw left Chelsea in fourth place, only one point ahead of in-form Newcastle United who sit just outside the Champions League spots in fifth and won 2-1 at Tottenham Hotspur earlier on Saturday.
Crystal Palace are 15th, six points ahead of Ipswich Town who are in the highest of the three relegation positions and travel to Fulham on Sunday.
After a first 45 minutes dominated by Chelsea, the hosts started the second half stronger with Eze going close from a cross by Ismaila Sarr in the 49th minute. Chris Richards forced Robert Sanchez into a reflex save seven minutes later.
Chelsea had their own chances when Enzo Fernandez and Nicolas Jackson both shot narrowly wide in the space of a minute before Mateta's equaliser.
The Blues had been aiming to get back to winning ways after losing to struggling Ipswich Town and west London neighbours Fulham and drawing 0-0 at Everton in their previous three matches, an abrupt loss of form that shattered talk of them mounting a title challenge.
Sancho said Chelsea coach Enzo Maresca had ordered his players to finish off the contest at halftime, something they failed to do with errant finishing.
"It's kind of frustrating to concede late in the game," the winger - who is on loan at Chelsea from Manchester United - told BBC radio. "We have to learn from this and move on. We have to finish our chances."