Manchester City piled pressure on Chelsea boss Graham Potter as Riyad Mahrez inspired a 4-0 rout in the FA Cup third round, while Aston Villa crashed to a stunning 2-1 defeat against fourth tier Stevenage on Sunday.
After Premier League sides Newcastle, Nottingham Forest and Bournemouth were humiliated by lower-league opposition on Saturday, Villa were rocked by Stevenage's two-goal blast in the final minutes.
Premier League champions City rarely suffer such embarrassment and they made the strongest possible start by dismissing abject Chelsea with contemptuous ease at the Etihad Stadium.
Pep Guardiola made seven changes from the City side that won 1-0 at Chelsea in the Premier League on Thursday.
But City were still far too dynamic for struggling Chelsea as Mahrez struck with a brilliant free-kick and a late penalty, with Julian Alvarez and Phil Foden also scoring.
In the fourth round, City will host Premier League leaders Arsenal or third-tier Oxford, who meet on Monday.
City had already eliminated Chelsea from the League Cup this season and the west London club's first FA Cup third-round exit since 1998 was another blow to a season in danger of spiralling out of control.
While it is probably too early for Potter to be fearing the sack, just four months after he arrived from Brighton to replace the axed Thomas Tuchel, the 47-year-old might be having a few sleepless nights as he wrestles with his team's woeful form.
Chelsea have won just three of their last 12 games in all competitions and sit 10th in the Premier League, 10 points adrift of the top four place the club's American owners would surely have expected Potter to deliver.
"The results in a small space of time are not positive. You can make excuses and look for reasons or say it isn't good enough. Both of those answers are correct," Potter said.
"We have to keep improving and stick together because clearly we are suffering as a football club and it's not nice at all."
Potter will hardly have been comforted by the sound of Chelsea fans chanting Tuchel's name as they pine for the German who led them to Champions league glory in 2021.
"I would tell (Chelsea co-owner) Todd Boehly to give Graham Potter time. All coaches need time. At Barca, I didn't need two seasons, but that's because I had Messi," Guardiola said.
Given Chelsea's predicament it was curious that Potter elected to make six changes, with Bashir Humphreys given his debut and fellow teenager Lewis Hall also starting.
Mahrez had scored the winner against Chelsea on Thursday and this time he bent a superb free-kick into the top corner in the 23rd minute.
Woeful Chelsea
City's second goal was a gift from Chelsea forward Kai Havertz, who punched the ball as he challenged Aymeric Laporte at a corner, with Alvarez converting the 30th minute penalty.
Chelsea were being torn apart and Foden hit the third goal in the 38th minute, the England forward finishing off Kyle Walker's cross.
Beaten in the last three FA Cup finals, Chelsea's misery was compounded in the 85th minute as Mahrez scored from the spot after Kalidou Koulibaly fouled Foden.