Leicester 2 Chelsea 4 (after extra-time)
Cesc Fabregas sent a reminder to Chelsea boss Antonio Conte as his extra-time double capped a fine comeback at 10-man Leicester.
The midfielder's quickfire brace completed the visitors' recovery as they battled from 2-0 down to win 4-2 after extra-time to reach the fourth round of the EFL Cup.
Fabregas has been marginalised by Conte since the boss' summer arrival and has not started in the Premier League this season but proved his worth, ahead of Saturday's Premier League visit to former club Arsenal.
Gary Cahill and Cesar Azpilicueta's stunning strike helped Chelsea come from behind after defensive howlers allowed Shinji Okazaki to score twice in the first half.
Leicester's Marcin Wasilewski was sent off a minute before the end of normal time as the hosts failed to build on their fine start.
Pedro had a fifth-minute goal disallowed for offside before the visitors started to hit the self-destruct button.
Cahill's heavy touch allowed Okazaki to steal the ball and Ahmed Musa nipped in and only a fortunate tackle by Luiz halted him but it was only a prelude to more Chelsea calamity which cost them after 17 minutes.
The Foxes had been quiet but Musa's cross caused chaos as Cahill failed to deal with it and the ball hit Azpilicueta.
It fell to Okazaki who nodded past the onrushing Asmir Begovic and the ball clearly crossed the line despite Azpilicueta's attempt to clear.
It meant Chelsea have kept just one clean sheet in their past 12 away games, against last season's whipping boys Aston Villa.
Michy Batshuayi headed Pedro's cross wide as they tried to respond but the lead allowed Leicester to settle and they cashed in on more hesitant defending after 34 minutes.
Pedro's awful half clearance only found Andy King who spotted Okazaki's run and, as Luiz failed to stop him, the striker's effort bounced past Begovic.
As bad as Chelsea and Cahill had been the defender hauled them back seconds before half-time when he headed in Pedro's corner as Danny Drinkwater tried to hack off the line.
It changed the complexion of the game and within four minutes of the re-start Chelsea levelled.
This time it was Leicester's turn to be defensively suspect when Wasilewski could only clear to Azpilicueta to launch a brilliant 20-yard volley into the top corner.
Level, Chelsea asserted their authority and Ron-Robert Zieler produced an outstanding stop to divert Batshuayi's rising drive after 66 minutes.
Diego Costa then replaced Ruben Loftus-Cheek and the striker should have put Chelsea ahead after 69 minutes when he raced onto Luiz's deep pass only to curl wide.
The improving visitors, with the tireless Pedro leading the charge, looked the more likely to win yet one long punt from Zieler caused huge problems and needed a fine Begovic save to deny Musa.
From the corner Andy King wasted a fine chance when he nodded over and the introduction of Jamie Vardy with 16 minutes to go unnerved Chelsea.
As the game opened up Luiz continued to look uncomfortable, with Vardy looming as a menace, while at the other end Zieler blocked Costa's angled effort before an even better double stop with seven minutes left.
Another long pass from Luiz released the Spain international and he shrugged off the challenge of Wasilewski to fire at Zieler and saw the goalkeeper palm his second effort behind.
Costa was then central again when Wasilewski was dismissed with a minute left.
The defender, already on a yellow card, produced a needless challenge on the striker in front of the dugouts as he led with his elbow to collect his second booking.
Costa then rifled into the side-netting but Chelsea only needed 71 seconds of extra-time to complete their comeback.
A neat interchange between Costa and Eden Hazard sent the midfielder scampering on the edge of the box and his backheel gift-wrapped the chance for Fabregas to fire in from 16 yards.
Two minutes later the midfielder wrapped the game up when he scored from 12 yards after the ball had ballooned up.