Chelsea suffered their eighth Premier League defeat of the season in a bruising 2-1 loss away to Fulham.
The Blues went down in the first half after former star Willian 's strike took a kind deflection off Trevoh Chalobah. Graham Potter 's rudderless side equalised two minutes after half-time through Kalidou Koulibaly, but it was about to all go wrong again for the under-fire English boss.
New signing Joao Felix, chucked in for his debut only a day after signing on loan from Atletico Madrid, ended a promising performance prematurely with a two-footed tackle which resulted in him being shown a red card. It didn't take long for Fulham to capitalise, as second-choice striker Carlos Vinicius - filling in for the suspended Aleksandar Mitrovic - made sure that the Cottagers would leapfrog Liverpool in the table and secure just their second victory over their West London rivals in 43 years.
Here are seven talking points from Craven Cottage.
1. Felix fast-tracked
Less than 36 hours after being confirmed as Chelsea's newest signing, Joao Felix arrived at Craven Cottage ready for action to the surprise of many. What shocked fans even more was that Graham Potter had decided to name the 23-year-old Portuguese forward in his starting lineup for a crucial Premier League clash.
Sporting the No.11 shirt, Felix strutted out to begin his sixth-month stay in West London as soon as possible. The Atletico Madrid loanee started brightly, too, drawing four fouls, getting two Fulham players booked, taking one shot and laying on what should've been an assist for Kai Havertz - all inside in the opening 15 minutes.
He even has his own song, with the away section at Craven Cottage bellowing soon after kick-off: "Joao Felix, woah, he comes from Portugal, he hates the Arsenal." Their fans won't be signing it for a while yet, though...
2. Willian still classy
Touted as one of the Premier League's best attackers not so long ago, Willian's return to West London from out in the wilderness has gone relatively under the radar. After a nightmare spell with Arsenal and return to Brazil with Corinthians, the 34-year-old winger has impressed since signing for Fulham on a free transfer in September.
A goal against Leeds earlier in the campaign reminded many that he's indeed back in the Premier League, but putting one past his former club may well go down as his landmark moment as a Cottager. Picking up the ball on the left, Willian stood up Trevoh Chalobah inside the penalty area and attempted to curve a shot into the bottom right-hand corner.
It didn't work out quite that way, but a deflection off the unfortunate Chalobah took the ball beyond Kepa Arrizabalaga and into the back of the net. Craven Cottage went wild with ecstasy, but the Brazilian stayed classy by refusing to celebrate, instead opting to respect the side who first brought him to England nearly a decade ago.
Chelsea had been creaking and it didn't take long for them to crack. As per Opta, the Blues have now had more former players (26) score against them than of any side in the Premier League. Talk about being haunted.
3. Leno following Willian's lead
Speaking of ex-Arsenal players proving themselves elsewhere, Bernd Leno is enjoying a superb first season away from the Emirates. After sealing a deal which could rise to £4million during the summer transfer window, the German goalkeeper has been outstanding for Fulham.
Going into the Chelsea clash with four clean sheets in 16 Premier League appearances, Leno picked up from where he left off and produced a string of saves to keep the Blues at bay. Firstly denying Havertz from close range, an excellent reaction stop from Lewis Hall prevented the visitors from equaliser just minutes after Willian's opener.
Although you'd be hard-pressed to find any Arsenal supporters keen to swap Aaron Ramsdale for their former No.1, Leno seems to have recovered from a difficult campaign sat on the bench for the Gunners and looks more like the man tipped for international stardom when he was coming up at Bayer Leverkusen.
4. Koulibaly turns the tide
One of the most criticised players of Chelsea's wretched season, Kalidou Koulibaly stood up to the task and made it 1-1 just two minutes after the break. Capitalising on Mason Mount's free-kick, the Senegalese powerhouse showed his prowess at the other end and drew the Blues level.
It was the first time that Chelsea scored a goal from a losing position since going behind to Dinamo Zagreb on November 2, eight games ago. Since then, they've rolled over and taken defeat five times in brutal fashion - but not this time.
5. Potter's familiar problem
Injuries, injuries and more injuries. Graham Potter just can't escape them. With a host of key players like Raheem Sterling, Reece James and N'Golo Kante already sidelined, the last thing that the Chelsea manager would've wanted to see after his side got back on level terms was another player to hobble off.
The Swiss midfielder, 26, went down off the ball in the second half to Potter's dismay and had to be subbed for Jorginho. Unfortunately for the Blues, though, what was about to happen was even worse.
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6. Off Joao go
Regardless of the scoreline, it all looked so promising for Joao Felix on his Chelsea debut. Tricky runs, sharp turns and neat passes were what Blues supporters had been hoping for from the Portugal international - certainly not two-footed tackles, though.
As the hour mark approached, Felix naively flew in studs-up on Fulham right-back Kenny Tete and gave referee David Coote no option but to show him a straight red card. Mild protests from Potter and his staff fell on deaf ears, and now they'll be without the attacking talent for three games - and it was the turning point here.
It seems you can take the boy out of a Diego Simeone side, buy you can't take the Simeone out of the boy.
7. Aleksandar who?
Ahead of the game, Fulham's excitement was tempered by the absence of star striker and talisman Aleksander Mitrovic. Scorer of 11 goals in 15 league games this season, the 28-year-old Serbian was suspended for picking up five yellow cards in the first half of the campaign.
So, perennial backup Carlos Vinicius came and more than made up for Mitrovic's absence. As the home side began to make their man advantage count with a period of sustained possession, the ex-Tottenham Hotspur flop rose highest to meet Man of the Match Andreas Pereira's delivery - which Arrizabalaga wasn't brave enough to make an attempt for - and pop a header over the Spanish goalkeeper, floating into the back of the Chelsea goal.
The Blues were soon beaten in league play for the eighth time this season, meaning that Potter's last win came the day after Boxing Day. It can surely only get better - more like how the Cottagers' magnificent season is going.
