Following a furious outburst after the final whistle, Calabria becomes the latest man booked by an increasingly flustered referee.
90' +3
A. Saelemaekers gets yellow.
Amir Rrahmani gets yellow.
Rrahmani was particularly aggrieved by Saelemaekers' attempts to buy a late penalty, and for then shoving his opponent he is shown a yellow card.
After trying to earn his side a penalty, Saelemaekers is confronted by Napoli players annoyed by his apparent simulation and his response earns the Belgian winger a booking.
90' +2
In the second minute of five indicated for stoppage time, Milan are probing gently inside Napoli's half when Leao loses patience and lashes a 25-yard shot well over the crossbar.
90'
Meret makes a straightforward save low down at his near post, after Leao shuffles inside, beats Di Lorenzo and drives a shot in from just outside the box.
85'
It's Milan on top now, as Napoli take up an unfamiliar defensive shape in order to limit their losses. There's still at least 90 minutes of this tie to come in Naples next week, after all.
81'
M. Politano enters the game and replaces K. Kvaratskhelia.
M. Olivera enters the game and replaces Mário Rui.
A weary Kvaratskhelia is also coming off, with fellow winger Politano thrown on for the final stages.
Spalletti now responds with a triple substitution. First, Ndombele comes in for Zielinski in midfield.
A straight swap at left-back sees Rui make way for the fresh legs of Olivera.
80'
A. Rebić enters the game and replaces Brahim Díaz.
T. Ndombélé enters the game and replaces P. Zieliński.
Having played a major part in creating Milan's goal, Diaz is now withdrawn; Rebic replaces him.
78'
Kim Min-Jae gets yellow.
Now the referee, who was apparently averse to booking players in the first half, shows yellow to a bemused Kim. Following a minor foul, it seems the centre-back is then booked for dissent.
77'
Following a Tonali layoff, Krunic scuffs an untidy attempt well wide of the right-hand post from 20 yards.
76'
Spalletti is now in something of a quandary, as his team still trail and are now short-handed. Should they still pursue an equaliser, or try to limit the damage ahead of next week's second leg?
Minute
Description
74'
F. Anguissa gets a second yellow card and is sent off.
Another mistimed challenge in midfield - his second in the space of a few minutes - sees Anguissa sent off! That's his second booking, as he makes contact with Hernandez's midriff with an outstretched boot. Napoli are down to 10 men!
73'
From 35 yards out, an awful free-kick by Rui sends the ball straight out of play, floating over the top of a packed Milan area.
71'
A rare Milan period of pressure sees Giroud fail to make contact with a trademark acrobatic effort, then he concedes a free-kick for pushing Kim inside the Napoli area.
70'
G. Di Lorenzo gets yellow.
F. Anguissa gets yellow.
For halting Hernandez with a clumsy challenge in midfield, Anguissa is shown a yellow card by the referee.
The referee also books Napoli captain Di Lorenzo, in his case for dissent.
69'
G. Raspadori enters the game and replaces H. Lozano.
After a quiet game, Lozano is taken off; making way for Raspadori to come on up front.
68'
After a layoff by Elmas, who has his back to goal on the edge of the area, Anguissa scuffs a shot wide of the target via a deflection off the stand-in striker's leg.
67'
A. Saelemaekers enters the game and replaces I. Bennacer.
Having recently been booked, Bennacer is withdrawn by Pioli. Saelemaekers - who excelled against Napoli as a substiute earlier this month - comes on.
66'
Quite confidently now, Milan stroke the ball around in front of their frustrated opponents. The Scudetto holders are showing their likely successors that they were crowned Serie A champions for a reason.
64'
Rui's outswinging corner from the left is headed away at the near post by Leao, and Milan just miss out on starting another counter-attacking raid in the aftermath.
62'
With a well-timed tackle, Milan captain Calabria saves his side at the last, as Kvaratskhelia dances inside from the left after picking up Zielinski's pass and tries to set up a shot. That's brilliant defending by the Rossoneri's right-back.
60'
I. Bennacer gets yellow.
For a foul on Anguissa in midfield, Bennacer becomes the first Milan player booked.
59'
Sitting very deep now, Milan are managing to halt Napoli's momentum and will perhaps feel confident of keeping yet another Champions League clean sheet.
55'
Tonali heavily overhits a free-kick from the right flank into the area, and a stretching Leao can only turn it behind on the left byline.
54'
Under little pressure, the imperious Maignan comfortably claims a drifted cross from the left by Zielinski and Napoli's latest attack fizzles out.
52'
Shortly after seeing a tame header simply saved by Maignan, Di Lorenzo has a mishit shot blocked behind by Kjaer's covering lunge. It's another corner for Napoli, who are totally on top now.
49'
It's been a more tentative start to the second half so far, in contrast to both the opening and closing stages of the first. Napoli are still having most of the ball.
47'
After a delay for the referee's communications kit to be fixed by his colleagues, the game gets back under way once he has had a chat with both captains.
46'
Milan kick off, and we are back under way at San Siro!
45' +4
HALF-TIME: MILAN 1-0 NAPOLI
45' +2
Tonali's second successive corner-kick is only part-cleared by Napoli's ailing defence, and it is now the Azzurri who are hanging on for the half-time whistle - how the goal has changed things!
45' +1
Diaz and Giroud combine on the right side of the area, before the latter lays the ball off for Tonali. The Milan midfielder strikes at goal, but sees his low shot deflected behind for a corner.
43'
Clipped by Lozano, who is clearly not on good terms with his direct opponent today, Hernandez takes the chance to hit the deck. There's no booking for the Mexican winger, though, or even a Milan free-kick. Pioli is outraged and is instead shown yellow near the touchline.
42'
Two fiery characters - Hernandez and Lozano - square up on the touchline, but after some exhanged words and glaring from several players on either side, the altercation fizzles out when the referee arrives on the scene.
40'
I. Bennacer has scored a goal for AC Milan! Assist by Brahim Díaz.
MILAN LEAD! Against the run of play, the seven-time champions strike! Diaz sprints through the centre at speed, exchanges passes with Leao, then tees up Bennacer. From 10 yards, the midfielder stays cool to fire the ball into the back of the net via Meret's foot for his first-ever Champions League goal! What a time to get it! It's 1-0 to Milan!
Turning two defenders near the halfway line, Diaz slips clear and then swaps passes with Leao inside the area before playing in goalscorer Bennacer.
38'
P. Zieliński gets yellow.
After exhibiting some leniency earlier in the game, the referee finally flashes his yellow card: Zielinski is booked for a hack on the shins of Krunic.
36'
Finally, Giroud is cleared to continue and returns to the fray from the sidelines. Now into the final 10 minutes of the first half, Milan will be glad to keep things level until the break.
34'
After taking a clattering from Kim, a pained Giroud writhes around on the soggy turf. The game comes to a halt while the French forward receives treatment.
32'
When Milan finally press forward in numbers, their attack ultimately falls apart, and Krunic crunches Zielinski down to the turf with a challenge designed to halt Napoli's counter. He avoids a booking, though.
31'
Due to Milan's attempts to nullify Napoli, the pace has certainly dropped over the past few minutes. The Rossoneri are mainly focused on retaining the ball inside their own half and pumping forward the occasional long ball.
29'
Spalletti is enraged by the touchline, as Anguissa fails to pick out Kvaratskhelia with a pass across to the left flank. It merely rolls out of play for a throw-in, and for all Napoli's supremacy, they've yet to make it pay by scoring that crucial first goal.
27'
Following an unusual delay for the corner flag to be repaired once Leao has dismantled it with a kick, the action resumes at San Siro.
25'
CLOSE! Brushing two defenders aside on the halfway line, Leao spots some space to sprint into - and takes it! The Milan forward powers clear to the edge of the box and then fires a low shot only a foot wide of the right-hand post! Brilliant individual play!
23'
From slightly further out than last time - perhaps 25 yards out on this occasion - Zielinski sends a shot spiralling over the crossbar, allowing Maignan to take a watching brief rather than springing back into action.
21'
The Azzurri shirts of the away side are again swarming all over the deep-lying Rossoneri, as Napoli continue to dominate the ball and press aggressively for an opening goal.
19'
After a typical surge up the left flank, Hernandez's claims for a free-kick on the edge of Napoli's area are turned down, and there was minimal contact from Lozano - if any.
17'
An ambitious low raking cross from the left by Rui drifts clear of Lozano and straight out of play for a Milan goal-kick, offering the struggling hosts some much-needed respite.
13'
Once again up from the back, Di Lorenzo leaps highest to reach a cross from Rrahmani with a long-range header, which loops up and finally drops on top of Maignan's net.
11'
JUST WIDE! Kvaratskhelia drives inside from the left, then after exchanging passes with Elmas inside the Milan area, lets fly with a shot that is deflected narrowly wide of the left-hand post by Kjaer's outstretched leg!
9'
On the stretch, just inside the Napoli area, Giroud can't quite take Leao's pacy throughball into his stride and the visitors have another goal-kick.
7'
Diaz wins a free-kick on the right, taken by Tonali and delivered into the box, but the masked Meret manages to punch the ball clear, then it's turned behind for a Napoli goal-kick.
5'
Milan are reeling at Napoli's lightning-fast start to the game, and seek a little control by keeping the ball for a sustained spell. They've survived an early storm and can now try to pose their own threat.
3'
CLOSE! Anguissa's powerful shot from the edge of the box forces Maignan to tip the ball over for a corner. Then, from the set-piece, Rui's inswinging cross is nodded wide by Napoli skipper Di Lorenzo at the near post!
1'
Napoli kick off, and we are under way in rainy Milan!
Hello and welcome to live coverage of today's Champions League quarter-final first leg clash between Milan and Napoli at San Siro!
Today, seven-time European champions Milan meet Napoli for the first time ever in the Champions League, seeking to emulate their shock 4-0 victory in Naples earlier this month. Quarter-finalists for the first time since 2012, Stefano Pioli's men eliminated Tottenham Hotspur in the last 16 and now tackle their fellow Serie A side in the final eight. Ahead of today's first leg, the Rossoneri - who could meet city rivals Inter in the semi-finals - have lost only one of nine previous all-Italian match-ups in UEFA competition.
Well down the road to succeeding today's hosts as Italian champions, a 22-point gap separates leaders Napoli from fourth-placed Milan in the Serie A standings. While 24 wins from 29 league fixtures so far places the Scudetto within tantalisingly close reach, Luciano Spalletti's side now want to break more new ground in Europe - this is the club's first-ever quarter-final appearance. A series of spectacular victories during the group stages were followed by last month's 5-0 aggregate defeat of Eintracht Frankfurt, and this season's Champions League's top scorers now arrive in Italy's second city having beaten Milan on each of their last three trips to San Siro.
MILAN (4-2-3-1): Mike Maignan; Davide Calabria, Simon Kjaer, Fikayo Tomori, Theo Hernandez; Sandro Tonali, Rade Krunic; Brahim Diaz, Ismael Bennacer, Rafael Leao; Olivier Giroud.
SUBS: Antonio Mirante, Matteo Gabbia, Fode Ballo-Toure, Junior Messias, Alexis Saelemaekers, Tommaso Pobega, Alessandro Florenzi, Malick Thiaw, Ante Rebic, Charles de Ketelaere, Pierre Kalulu, Divock Origi.
NAPOLI (4-3-3): Alex Meret; Giovanni Di Lorenzo, Kim Min-Jae, Amir Rrahmani, Mario Rui; Frank Anguissa, Stanislav Lobotka, Piotr Zielinski; Hirving Lozano, Eljif Elmas, Khvicha Kvaratskhelia.
After an airing of the iconic Champions League anthem, both teams are taking up their places on the San Siro pitch, and kick-off is now just moments away!
Not only did they hold Napoli goalless when the teams met in Naples earlier this month, but Milan have a record of W4, D0, L0 when leading at half-time in this season's Champions League. Today, they are seeking a fifth straight clean sheet in the competition - that would ensure a lead for next week's return leg at Stadio Maradona.
While Milan visit Bologna at the weekend and Napoli must tackle Serie A strugglers Verona, the teams reconvene in Campania six days from now, to decide who will reach the Champions League semi-finals.
That's all from San Siro today, so thank you for joining us and goodbye!
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