A second-string Nottingham Forest side took a major step towards Premier League survival by inflicting Chelsea's sixth consecutive league defeat.
Forest boss Vitor Pereira made eight changes with Thursday's Europa League semi-final second leg against Aston Villa in mind, but two goals from Taiwo Awoniyi and another from Igor Jesus helped the visitors open a six-point gap over 18th‑placed West Ham in the relegation zone.
Chelsea, meanwhile, scored a late consolation goal through striker Joao Pedro, narrowly avoiding an unwanted record of making it six league games in a row without scoring for the first time in the club's history.
Their dismal afternoon was summed up when Cole Palmer missed a first-half penalty after academy winger Jesse Derry, 18, suffered a serious-looking head injury on his first senior start.
It was Chelsea's first Premier League match since Liam Rosenior was sacked, with interim head coach Calum McFarlane - who guided the club to a 1-0 FA Cup semi-final win against Leeds United last week - taking charge for the first time at Stamford Bridge.
Forest needed just two minutes to take the lead, with Awoniyi left unmarked to head home after winger Dilane Bakwa beat Chelsea defender Marc Cucurella and delivered a nicely floated cross.
The same Forest pairing combined again in the 15th minute to win a penalty. Awoniyi was pulled back in the area by Malo Gusto as he attempted to reach Bakwa's cross, and Igor Jesus converted the resulting spot-kick straight down the middle. It came after a video assistant referee (VAR) check, with Gusto possibly lucky to have avoided a red card.
Enzo Fernandez hit the post and Igor Jesus forced a good save at the other end, before Derry won Chelsea a penalty following a nasty head collision with Zach Abbott that led to a six-minute stoppage and both academy graduates being substituted.
Palmer's low penalty kick towards the corner was then saved by Forest goalkeeper Matz Sels at full stretch.
Chelsea introduced striker Liam Delap for Derry and returning defender Levi Colwill at half-time, but conceded again seven minutes into the second half when Awoniyi tapped in substitute Morgan Gibbs-White's low cross.
Gibbs-White was later involved in another heavy clash of heads with Chelsea goalkeeper Robert Sanchez, with both players forced off with their bleeding heads bandaged.
Chelsea striker Joao Pedro also had a goal narrowly ruled out for offside late on, but then scored a spectacular overhead kick in stoppage time to end Chelsea's more than 550-minute run without a league goal that stretched back to early March.
Forest remain 16th but have significantly strengthened their survival prospects, while Chelsea stay ninth and 10 points adrift of the Champions League places - with qualification a target set at the start of the season.
BBC