Former Chelsea midfielder Willian had given Fulham a 25th-minute lead against his former club before Kalidou Koulibaly scrambled home an equaliser two minutes into the second half.
But Felix, who was enjoying an impressive debut following his loan move from Atletico Madrid, cut short Chelsea’s comeback when his high tackle on Kenny Tete just before the hour mark saw the Portugal forward shown a red card.
Fulham took advantage of their numerical advantage as Carlos Vinicius, in for the suspended Aleksandar Mitrovic, made the most of more poor Chelsea defending to head home the winner in the 73rd minute.
The goal was enough to give Fulham their fourth win in a row in the top flight for the first time since 1966 and takes Marco Silva’s impressive side above Liverpool and into the top six, though having played two games more. They are also now six points above a Chelsea team that remain languishing down in 10th spot.
And the pressure is sure to only increase on Chelsea boss Graham Potter after a third straight defeat in all competitions, to leave them with just one win in their last nine Premier League outings.
There was more misery for Potter, too, besides the result. Not only will he now lose Felix for three games to suspension but he also saw midfielder Denis Zakaria suffer a second-half injury to add to Chelsea’s mounting list of absentees.
In contrast, the night had all started so brightly for Chelsea and Felix.
Despite only completing his loan move to Stamford Bridge just over 24 hours earlier, Felix immediately showed Chelsea fans what he has to offer to a struggling attack.
Within two minutes, he created a golden opportunity, breezing past Tim Ream down the right to cut into the box and pick out Kai Havertz, whose low shot was blocked before Lewis Hall failed to make the most of an even clearer chance off the rebound.
Playing off of Havertz up front and linking up well with the Germany forward, the only thing missing from Felix’s first 45 minutes was a goal.
Three times he had efforts in the first half but failed to find the net. The best of those openings came five minutes before the interval when, from Havertz’s layoff, his shot produced a fine reaction save down low by Bernd Leno in the Fulham goal.
It was a former Chelsea attacker, though, who did find the target as Chelsea’s defending was found wanting. Only two minutes after escaping when an errant header from Trevoh Chalobah gifted a chance to Bobby De Cordova-Reid, whose effort clattered the crossbar, Chelsea fell behind.
Chalobah was again at the heart of some unconvincing defending, as his attempted headed clearance only helped a deep cross onto Willian at the back post. The Brazilian veteran was then allowed to cut in on his favored right foot before unleashing a low shot that deflected off Chalobah and in off the far post to give Fulham the lead.
Staring at a fifth loss in their last seven Premier League outings, Chelsea, and Potter, desperately needed a response in the second half.
With a touch of fortune, they got just what they needed just after the restart.
Mason Mount was the architect with a clever free-kick from wide on the left that caught out Leno at his near post, bouncing off the woodwork and falling for Koulibaly, who scrambled the ball over the line despite the Fulham goalkeeper’s desperate attempt to keep it at bay.
But just as quickly as Chelsea began turning things around, it all went wrong for Potter once more.
Moments after losing Zakaria to injury, Felix could have no complaints after he slid in high and studs-up onto the knee of Tete to give referee David Coote little choice but to produce a red card.
Fifteen minutes later Chelsea paid the price. Andreas Pereira, for a pinpoint cross, and Vinicius, for a towering back-post header, both deserve plaudits, but there was plenty to criticise once more in the visitors’ defending and goalkeeper Kepa Arrizabalaga getting caught in no-man’s land.
Chelsea had little answer and will now have to wait until Sunday’s home clash with Crystal Palace to try to arrest their slide.