Chelsea fell to Brentford for the first time since 1939, as Christian Eriksen led the Bees to a 4-1 victory that should ensure their Premier League safety.
The European champions had taken the lead at Stamford Bridge early in the second half thanks to Antonio Rudiger's spectacular long-range shot, but they crumbled to lose for the first time since owner Roman Abramovich was sanctioned by the UK government.
Vitaly Janelt equalized a minute later, kicking off a 10-minute scoring rampage for the visitors.
Since his return to competitive football following a heart episode on the field during Euro 2020, Eriksen has been in excellent form.
During his international comeback for Denmark, the former Tottenham midfielder scored twice in as many games and completed the turnaround by lifting the ball over Edouard Mendy.
On the hour mark, Janelt made it 3-1 with a beautiful dink over Mendy.
Third-placed Chelsea is still on track to finish in the top four, but they will need to step up their game in the Champions League quarterfinals against Real Madrid on Tuesday.
Yoane Wissa finished off a great afternoon for Thomas Frank's side with a fourth goal, taking advantage of more ridiculous Chelsea defending.
Brentford has moved up to 14th place, 11 points clear of the relegation zone, after winning their third game in a row.