Jorginho (left) has scored seven of his eight Champions League penaltiesChelsea enjoyed a comfortable victory at AC Milan after former Blues defender Fikayo Tomori received an early red card.
Tomori was sent off for pulling back Mason Mount in the area, with Jorginho converting the penalty.
Pierre-Emerick Aubameyang doubled the lead with a confident strike against his former club.
But Chelsea and England suffered a blow in the second half when right-back Reece James limped off.
The win continues Graham Potter's unbeaten start as Chelsea manager, with four wins in his first five games.
It moves Chelsea top of Group E with seven points from four matches, but it remains extremely tight with Red Bull Salzburg on six points and both Milan and Dinamo Zagreb on four.
Bad night for Tomori and James
Tomori has not enjoyed his reunion with his boyhood club over the past couple of games - after Milan were beaten comprehensively at Stamford Bridge last week, the Chelsea youth product lasted just 18 minutes on Tuesday.
What looked like being a tight game was blown open when Tomori put his arm on the shoulder of England team-mate Mount, putting the midfielder off balance enough to send him tumbling to the floor.
Referee Daniel Siebert, who was central to the drama throughout to the ire of the home support, deemed it enough contact to be a penalty and that Tomori had not attempted to play the ball, thus overriding the double jeopardy rule and causing him to show the red card.
The decision was debated long and hard by Tomori and Milan's players, but eventually he had to leave the field and after a lengthy delay Jorginho calmly slotted the penalty away.
"I definitely don't think the referee has had one of his better evenings," said Milan boss Stefano Pioli.
He added: "The penalty and red card changed everything.Chelsea didn't need to play with a numerical superiority.
"I don't want to review the episode, it seems too obvious. I don't want to comment. I told the referee what I think, I don't speak English very well but I think he understood."
Mount was excellent for the first 45 minutes before being substituted for Conor Gallagher at half-time, having picked up a booking for arguing with Olivier Giroud in the aftermath of the penalty.
Potter decided to remove Mount from the firing line of both the irate home fans and the card-happy Siebert - but not before the England midfielder caused Milan endless problems and showed why he is so admired by his managers for club and country.
While his form is a boost for Gareth Southgate, the sight of James hobbling off minutes after jarring his knee in the turf while making a challenge is worrying, with the World Cup less than six weeks away.
Having been so well stocked at right-back previously, Southgate is now sweating on the fitness of James as well as Kyle Walker and Trent Alexander-Arnold, who have all suffered injuries in recent weeks.
Four in a row for Potter
Only two players have started all five of Potter's games in charge of Chelsea so far - goalkeeper Kepa Arrizabalaga and Mount.
The latter was central to the second goal too. He was played the ball on the edge of the Milan area by Jorginho, and cleverly laid it off first time. Both Raheem Sterling and Aubameyang were running on, and the former smartly moved out of the way for the latter to plant the ball beyond Ciprian Tatarusanu at his near post.
From then on it was fairly straightforward for Chelsea to earn only their second competitive win on Italian soil from 15 attempts, the last being a 4-0 victory for Claudio Ranieri's side at Roberto Mancini's Lazio in November 2003.
They came the closer of the two sides to scoring in the second half, with Gallagher hitting the side-netting after rounding Tatarusanu.
It is a fourth successive win for Potter, with Chelsea continuing an impressive turnaround by rising to the top of Group E after four games, having been bottom after matchday two.
Line-ups
AC Milan
Formation 4-2-3-1
1Tatarusanu
20Kalulu46Gabbia23Tomori19Hernández
4Bennacer8Tonali
10Díaz33Krunic17da Conceição Leão
9Giroud
1Tatarusanu20Kalulu46GabbiaBooked at 32mins23TomoriBooked at 18mins19HernándezSubstituted forBallo-Touréat 80'minutesBooked at 90mins4BennacerSubstituted forPobegaat 62'minutesBooked at 66mins8TonaliBooked at 89mins10DíazSubstituted forDestat 37'minutes33KrunicBooked at 35mins17da Conceição LeãoSubstituted forOrigiat 80'minutes9GiroudBooked at 20minsSubstituted forRebicat 62'minutesSubstitutes
5Ballo-Touré12Rebic21Dest27Origi30Messias32Pobega83Mirante93Coubis96JungdalChelsea
Formation 3-4-2-1
1Arrizabalaga
14Chalobah6Thiago Silva26Koulibaly
24James8Kovacic5Jorginho21Chilwell
19Mount17Sterling
9Aubameyang
1Arrizabalaga14Chalobah6Thiago Silva26Koulibaly24JamesSubstituted forAzpilicuetaat 62'minutes8Kovacic5Jorginho21ChilwellSubstituted forCucurellaat 89'minutes19MountBooked at 20minsSubstituted forGallagherat 45'minutesBooked at 86mins17SterlingBooked at 29minsSubstituted forLoftus-Cheekat 62'minutes9AubameyangSubstituted forHavertzat 79'minutesSubstitutes
10Pulisic12Loftus-Cheek13Bettinelli16Mendy18Broja20Zakaria23Gallagher28Azpilicueta29Havertz30Chukwuemeka32CucurellaReferee:Daniel SiebertAttendance:75,051Live Text
Match ends, AC Milan 0, Chelsea 2.
Second Half ends, AC Milan 0, Chelsea 2.
Offside, Chelsea. Ruben Loftus-Cheek tries a through ball, but Kai Havertz is caught offside.
Attempt blocked. Ruben Loftus-Cheek (Chelsea) right footed shot from the centre of the box is blocked. Assisted by César Azpilicueta.
Foul by Trevoh Chalobah (Chelsea).
Divock Origi (AC Milan) wins a free kick in the attacking half.
Attempt blocked. Ante Rebic (AC Milan) right footed shot from outside the box is blocked. Assisted by Tommaso Pobega.
Attempt saved. Divock Origi (AC Milan) right footed shot from the left side of the box is saved in the bottom left corner. Assisted by Ante Rebic.
Fodé Ballo-Touré (AC Milan) is shown the yellow card for a bad foul.
César Azpilicueta (Chelsea) wins a free kick on the right wing.
Foul by Fodé Ballo-Touré (AC Milan).
Substitution, Chelsea. Marc Cucurella replaces Ben Chilwell.
Sandro Tonali (AC Milan) is shown the yellow card for a bad foul.
Ben Chilwell (Chelsea) wins a free kick in the attacking half.
Foul by Sandro Tonali (AC Milan).
Attempt missed. Ben Chilwell (Chelsea) left footed shot from outside the box misses to the right. Assisted by Jorginho.
Conor Gallagher (Chelsea) is shown the yellow card.
Hand ball by Kai Havertz (Chelsea).
Foul by Ruben Loftus-Cheek (Chelsea).
Sandro Tonali (AC Milan) wins a free kick in the defensive half.
Player of the match
MountMason Mount
AC Milan
Squad number9Player nameGiroud
Squad number17Player nameRafael Leão
Squad number1Player nameTatarusanu
Squad number20Player nameKalulu
Squad number23Player nameTomori
Squad number19Player nameHernández
Squad number8Player nameTonali
Squad number4Player nameBennacer
Squad number10Player nameDíaz
Squad number46Player nameGabbia
Squad number21Player nameDest
Squad number33Player nameKrunic
Squad number27Player nameOrigi
Squad number32Player namePobega
Squad number12Player nameRebic
Squad number5Player nameBallo-Touré
Chelsea
Squad number19Player nameMount
Squad number24Player nameJames
Squad number8Player nameKovacic
Squad number6Player nameThiago Silva
Squad number5Player nameJorginho
Squad number26Player nameKoulibaly
Squad number9Player nameAubameyang
Squad number21Player nameChilwell
Squad number14Player nameChalobah
Squad number1Player nameArrizabalaga
Squad number23Player nameGallagher
Squad number28Player nameAzpilicueta
Squad number12Player nameLoftus-Cheek
Squad number17Player nameSterling
Squad number29Player nameHavertz
Squad number32Player nameCucurella
