Shinji Okazaki put the champions in command but a superb comeback saw the Blues progress with the midfielder scoring twice after the hosts had been reduced to 10 men
Chelsea recovered from two goals down to beat Leicester 4-2 at the King Power Stadium thanks to two goals in extra-time from Cesc Fabregas.
The visitors’ defence was highly culpable as Shinji Okazaki ended a 13-game goal drought with two first-half goals for the Premier League champions, but two of Antonio Conte’s back four were able to make amends either side of the interval.
Captain Gary Cahill headed home a Fabregas corner in first-half stoppage time before Cesar Azpilicueta – who tried in vain to hack both Okazaki goals off the line – elevated a pulsating match further with a spectacular long-range volley in the 49th minute.
Leicester were forced to play the additional half-hour with 10 men after Marcin Wasilewski struck substitute Diego Costa with a forearm and Chelsea made merry against reduced numbers as Fabregas struck twice inside the opening four minutes of extra-time.
The match took place following conflicting reports of Chelsea owner Roman Abramovich’s displeasure regarding last Friday’s 2-1 loss to Liverpool, meaning Conte’s men turned in a timely showing of character and class.
Marcos Alonso was selected for his Chelsea debut as both managers made seven changes and it was the reshuffled visitors who settled quickest.
Pedro had an early goal chalked off for a marginal offside and Wasilewski breathed easily when referee Robert Madley did not punish him for handling inside the box.
There was a similar sense of relief for Cahill when his pass was intercepted by Okazaki and his subsequent collision with Ahmed Musa in the penalty area went unpunished.