Brighton & Hove Albion beat Chelsea for the first time in the Premier League on Saturday afternoon, with the Seagulls recording a 4-1 victory over Graham Potter's side in East Sussex.
It proved to be an unhappy return to the Amex for Potter, who left Brighton at the start of September to take charge of Chelsea.
The result has left the London club in fifth position in the table, while Brighton are now up into seventh, with Roberto De Zerbi's side securing their fifth league victory of the campaign.
The Seagulls were three goals ahead in the first half of the match, and there was to be no fightback for Chelsea despite Kai Havertz registering early in the second period to give the visitors some hope of a comeback.
Thiago Silva made two excellent blocks in the early stages, first heading a Trossard effort off the line in the third minute before blocking a strike from Pervis Estupinan from the resulting corner.
Brighton managed to make the breakthrough in the fifth minute, though, when Trossard showed excellent feet inside the Chelsea box to round Kepa Arrizabalaga and find the bottom corner of the net.
Chelsea then found themselves two goals behind in the 14th minute, with Ruben Loftus-Cheek scoring an own goal when attempting to clear a dangerous corner from Solly March.
The visitors had two big chances to halve the deficit in the 18th minute, but Conor Gallagher saw his effort saved by Robert Sanchez before Christian Pulisic fired the rebound wide.
Sanchez made another save to keep out an effort from Gallagher in the 20th minute, before Moises Caicedo hit the post down the other end, with the home side threatening a third.
Brighton did manage to make it 3-0 in the 42nd minute when Estupinan's low cross was turned into the back of his own net by the sliding Trevoh Chalobah.
Chelsea had a goal back in the 48th minute of the contest, with Havertz heading a brilliant cross from Gallagher past Sanchez from close range.
Brighton managed to regain control in the period that followed, but Sanchez needed to make another smart save 20 minutes from time to prevent Pierre-Emerick Aubameyang's effort from finding the back of the net, before Julio Enciso passed up a good chance for the home side 10 minutes from time.
The Seagulls had a fourth in the second minute of added time at the end of the 90, though, with Pascal Gross adding gloss to the scoreline by registering from inside the box.
Chelsea will face Dinamo Zagreb in the Champions League on Wednesday before hosting Arsenal in the Premier League next weekend, while Brighton will be bidding to build on the strong result when they head to Wolverhampton Wanderers.
No Data Analysis info
Germany
Switzerland
Hungary
Scotland
Spain
Italy
Croatia
Albania
England
Denmark
Slovenia
Serbia
Austria
France
Netherlands
Poland
Romania
Slovakia
Belgium
Ukraine
Portugal
Turkey
Czech Republic
Georgia