Wesley Fofana gave Chelsea a first half lead before his night ended prematurely because of injury, with Pierre-Emerick Aubameyang and Reece James going on to add second and third goals.
Early on, a confident Milan hardly looked like the visitors with a decent start to the game, although it was Mason Mount who enjoyed the best chance when he sent Ciprian Tatarusanu sprawling low to his left to beat away a shot bound for the bottom corner.
A flurry of Chelsea set-pieces midway through the first half presented the hosts with another good opportunity, but Tatarusanu was equal to Thiago Silva’s header.
It was clear though that it could be a way through for Chelsea and indeed it led to a goal when Silva got his head to another delivery a few moments later. Tatarusanu could this time only weakly parry the ball back into danger and Fofana gladly pounced on the rebound for a tap-in.
Mount did have the ball in the net at the half hour mark, cleverly lifting the ball over Tatarusanu, but the Chelsea player had been offside when he was put through.
However, despite coming to dominate, the fragility of a 1-0 lead showed when Rade Krunic blazed a glorious Milan chance over the crossbar in first half stoppage time. It was similar to Chelsea’s opener on the rebound after a weak parry, but Krunic didn’t have Fofana’s accuracy or composure.
Ultimately, Milan’s initial promise faded quite badly and Chelsea’s second goal early in the second half was the result of a pretty woeful attempt at defending. Fode Ballo-Toure ambled to close down a James cross from the right, while Fikayo Tomori completely misjudged things to allow Aubameyang an easy finish from close range.
Milan’s collapse signalled Chelsea’s third. The Rossoneri were all over the place as Chelsea moved the ball quickly and Raheem Sterling fed the advancing James into right-hand side of the penalty area. His near-post finish was clinical, albeit poor from Tatarusanu.
Both managers made the maximum number of changes, which ultimately slowed and killed any chance of rhythm the game had. That probably suited Chelsea in the end because it allowed them to just sit on their lead. Milan, knowing the result was done, basically obliged.