Chelsea fought back from two goals down to beat Leeds in a nine-goal Carabao Cup thriller at Stamford Bridge, as substitutes Cole Palmer, Morgan Rogers and Pedro Neto inspired the comeback.
Defender Tarik Muharemovic headed the opener in the third-round tie as Leeds dominated the first half before Brenden Aaronson doubled the visitors' lead shortly after the break.
However, Chelsea manager Xabi Alonso's changes at the start of the second half ultimately transformed the contest.
Palmer scored from the penalty spot and curled home from the edge of the area in a pivotal two-minute spell before Neto added a third.
Rogers also played a key role, helping to create four goals from open play, with Danny Welbeck and Valentin Barco both benefiting.
Welbeck deflected Barco's wayward strike into the net in stoppage time to add a sixth Chelsea goal.
It was a remarkable turnaround, with both sides heavily rotated following their Premier League fixtures. Chelsea made nine changes, while Leeds made eight.
Leeds' second-string side were the better team throughout the first half, aside from a couple of efforts from Jamie Gittens and a flicked attempt from Welbeck shortly before the break.
Otherwise, Daniel Farke's side were in complete control. Aaronson and Muharemovic both had close-range efforts well saved by Chelsea goalkeeper Mike Penders in the 21st minute.
Muharemovic made the breakthrough moments later, powering a header in at the far post from a corner. He then missed a similar opportunity before midfielder Sean Longstaff fired over from the edge of the area.
In response, Alonso introduced Palmer, Rogers, Neto and Reece James for the second half, withdrawing 16-year-old debutant Reggie Watson, the fourth-youngest player to play for Chelsea, along with Malo Gusto, Gittens and Estevao Willian.
Leeds doubled their advantage when Ethan Ampadu capitalised on Barco losing possession in midfield. His cross was cut back and flicked into Aaronson's path, allowing the American to finish, but Chelsea soon responded.
The hosts were handed a lifeline when Dan James was adjudged to have fouled Pep Chavarria. Palmer swept the resulting penalty beyond Leeds debutant goalkeeper Michael Zetterer.
Two minutes later, Palmer curled a shot past Zetterer after Rogers flicked on Josh Acheampong's throw-in.
James then clipped a one-on-one chance just wide before Chelsea hit the front thanks to Neto. The Portugal forward slotted home on the counter-attack after being released by Palmer and Rogers.
Moments before Leeds were due to make four substitutions of their own, having also rested a number of regular starters, Welbeck added a fourth Chelsea goal by turning inside the area and drilling a low shot past Zetterer.
Two substitutes combined for Leeds as Dominic Calvert-Lewin guided Noah Okafor's cross into the corner, giving the visitors brief hope.
However, Barco then added a fifth Chelsea goal through a powerful finish after another delivery from Rogers, before Welbeck completed the flurry of scoring just before the final whistle.
Chelsea move into the fourth round, with ties to be played in late October.