This is the sort of result to make everyone sit up and take notice.
On a night of drama and controversy, Chelsea ran riot in the San Siro which is still one of Europe’s most formidable stadiums.
And in the space of seven days with back-to-back wins over AC Milan, Graham Potter has unquestionably shown his credentials to be Chelsea manager.
There was more than a slice of good fortune in Chelsea’s victory as German referee Daniel Siebert harshly sent off Fikayo Tomori which reduced Milan to ten men after just 20 minutes.
It has been a horrible week for Milan’s ex-Chelsea defender as he had a stinker against his old club at Stamford Bridge last week and then got a red card this time.
Tomori must have looked at these two games with Chelsea as a chance to show England boss Gareth Southgate what he can do before the World Cup squad is named on November 10.
Instead, Tomori - who was arguably the best defender in Serie A last season when Milan won the title - has seen his hopes left in tatters and Chelsea turn their Champions League fortunes around.
But even without the help of a dodgy ref determined to make himself the centre of attention, Chelsea still produced an impressive display and their own moments of brilliance.
Pierre-Emerick Aubameyang seems to have got his mojo back as he finished off a quite magnificent flowing move for Chelsea’s second goal.
Chelsea boss Potter said in the build-up that results against Europe’s best would help convince the players of his methods.
Well, there was no better proof that they are buying into Potter because this was their third straight win under the new manager and two of them have come against the Italian champions.
That is some statement and some start.
Chelsea were bottom of Group E after two games, before their double header with Milan, now they are top and look certain to qualify for the knock-out stages.
Milan have been decimated by injuries and were left cursing their luck again when Mason Mount got on the wrong side of Tomori. Mount was bearing down on goal, Tomori nibbled, pushed and put his arm on his ex-team mate but still no-one was really appealing.
Referee Siebert surprised everyone by not just giving a penalty but also showing Tomori a red card. The “double jeopardy” law has been removed but a player can still be sent off if they have not made a genuine attempt to play the ball. It looked soft on both counts.
Tomori was shell shocked, he was still remonstrating with the fourth official as Jorginho stepped up to score the penalty with his familiar hop, skip and a jump routine.
The San Siro had been rocking to all the pre-match Euro rock but now it was full of anger which only got worse as Olivier Giroud missed a big chance while Siebert seemed to be on a one-man mission to book as many players as possible as he was rapidly losing control.
Then came Chelsea’s second goal after 34 minutes following a lovely move. Mateo Kovacic swapped passes with Mount, Raheem Sterling was about to shoot when Aubameyang raced in, took the ball off his team mate’s toe and fired into the bottom corner.
Chelsea could have had more but the result was impressive enough without.
