Olivier Giroud's first-half strike proved the difference as Milan battled through to the Champions League last four with a 1-1 draw at Napoli to secure a 2-1 aggregate triumph.
Ismael Bennacer's goal last week at San Siro snatched a 1-0 quarter-final lead and Milan deservedly doubled their aggregate advantage in the first half on Tuesday in Naples.
Giroud had an earlier penalty saved by Alex Meret but made amends soon after with his 43rd-minute opener after Rafael Leao's incredible run to create the goal.
Victor Osimhen's stoppage-time strike offered Napoli hope after Khvicha Kvaratskhelia's 82nd-minute penalty was saved by Mike Maignan, but Milan held on to reach their first Champions League semi-final since 2007.
Matteo Politano twice whistled early efforts narrowly wide but the Rossoneri should have struck first when a clumsy Mario Rui lunge on Leao offered Milan a glorious chance from 12 yards.
Yet Meret guessed the right way to deny Giroud's spot-kick towards the bottom-right corner, before again thwarting the France veteran after another tame effort from a gilt-edged opportunity.
The Milan striker made no mistake next time round as Leao showed a remarkable turn of pace down the left before rolling across to Giroud for the simplest of tap-ins.
Victor Osimhen saw a strike ruled out for handball on the stroke of half-time and Kvaratskhelia blasted just over after the interval as Napoli searched for a response.
A Fikayo Tomori handball afforded Napoli a late opportunity to fight back into the clash, though Maignan dived low to his right to thwart Kvaratskhelia.
That penalty miss proved Osimhen's late header from Giacomo Raspadori's cross in vain as Milan battled through to the last four.
What does it mean? Milan frustrate Napoli once more
Runaway Serie A leaders Napoli have been by far and away the dominant force in Italy this season, yet Milan have had the edge over Luciano Spalletti's side.
The Rossoneri defeated Napoli twice in April, yet this draw will likely serve as the most punishing blow after Spalletti's men were sent crashing out of Europe in front of their vociferous home supporters.
A potential semi-final meeting with city rivals Inter awaits for Milan if the Nerazzurri can overcome Benfica in Wednesday's second leg. Simone Inzaghi's side lead the tie 2-0.
Giroud emulating fellow veteran Ibrahimovic
Giroud became the first Milan player to see a Champions League penalty saved since the 2005 final when Liverpool's Jerzy Dudek denied Andriy Shevchenko in the shootout, yet the France striker responded well.
The Milan striker's strike took him onto seven goal involvements in 10 European outings this term, only Zlatan Ibrahimovic has managed more for the Rossoneri in a single Champions League campaign (nine in 2011-12).
Not so super Mario
Rui had a game to forget after needlessly giving away the first-half penalty for an unnecessary and ill-timed lunge on Leao.
The left-back was fortunate to see his blushes spared by Meret but was forced off injured after just 34 minutes, having already lost possession a team-high nine times in a poor showing.
What's next?
Napoli return to Serie A action at Juventus on Sunday, when Milan host Lecce.
Alcaraz's pursuit for third straight Madrid Open crown continues
Carlos Alcaraz boosted his hopes of a third straight Madrid Open title as he comfortably beat Thiago Seyboth Wild to reach the fourth round on Sunday.
Back in his home country of Spain, Alcaraz eased to a 6-3 6-3 triumph to set up a fourth-round clash with Jan-Lennard Struff, whom he beat in last year's final.
The first six games of the opening set went to serve, but Alcaraz found a crucial break in the seventh and ninth games of the set to put him in pole position for victory, a lead he would not relinquish as he overcame being broken in the seventh game of the second set to seal his safe progression.
Holger Rune was a surprise casualty as the world number 12 was defeated 6-4 4-6 6-3 by Tallon Griekspoor, though world number eight Andrey Rublev eased through with a straight-sets win over Alejandro Davidovich Fokina.
Data Debrief
With his triumph over Seyboth Wild at the Madrid Open, Alcaraz has now won 93.3 per cent of his games at the tournament. That is the highest win percentage of any player with at least 10 games played in a single ATP-1000 event since the format was introduced in 1990.
Against Seyboth Wild, Alcaraz won 27 of his 31 first-serve points, also recording 19 winners to his opponent's 10 as he dominated the contest on his way to victory.
Bristol City Women 0-4 Man City Women: Hosts relegated as Fowler double inspires WSL leaders
Mary Fowler scored twice to set WSL leaders Manchester City on their way to a 4-0 rout of Bristol City, who suffered relegation as a result, on Sunday.
With Arsenal having drawn with Everton earlier in the day, Man City knew a victory would be enough to take the title race down to two teams.
That victory duly arrived in emphatic fashion, with all four of Man City's goals arriving in the second half.
Fowler's fantastic strike opened the scoring in the 62nd minute, with the Australia international doubling her tally soon after, paving the way for an Amy Rodgers own goal and Alex Greenwood's late header to seal a huge victory.
Arsenal are now out of the title race, with Chelsea - who have two games in hand on Gareth Taylor's team - the only side capable of catching Man City.
The Robins, meanwhile, will be playing in the second tier again next term.
Data Debrief: Bristol heading down with a whimper
Bristol City have failed to score in their last five games in the WSL, a run of 544 minutes without a goal.
They mustered just 0.09 expected goals (xG) to Man City's 3.4, with the visitors having now kept a clean sheet in nine of their 20 league games this season.
De Rossi demands more from 'tired' Roma ahead of crunch run
Daniele De Rossi acknowledged his Roma team may be tired, but he insisted they must not allow themselves to be embarrassed.
Roma fought back to draw 2-2 with last season's Serie A champions Napoli in a pulsating fixture on Sunday.
Tammy Abraham's late header secured a point for De Rossi's team, who took the lead through Paulo Dybala's penalty before going behind to goals from Matias Olivera and Victor Osimhen.
With Serie A set to have five teams in the Champions League next season, Roma occupy fifth spot with four matches remaining, but sixth-placed Atalanta are just two points behind with a game in hand.
There is also the small matter of a Europa League semi-final against Bundesliga champions Bayer Leverkusen on the cards over the coming weeks, and De Rossi set the stall out.
"We drew, it is not a result to throw away, but it is not the result or the performance that we wanted," Roma coach Daniele De Rossi told Sky Sports Italia.
"At times you can steal the ball off Napoli, but we then gave it back again too many times. Napoli had a lot of chances in the first half, we did better in the second, but we have to do better.
"Look, we are tired, but we cannot start thinking that we’re tired and that means we can be embarrassed in the final few weeks of the season."
Roma host Leverkusen on Thursday before taking on Juventus on May 5, with a crunch clash against Atalanta – who are also into the Europa League semi-finals – set to follow after the away leg against Xabi Alonso's team.
Key to a successful end to the campaign for Roma will be keeping Dybala fit. The Argentine has been involved in the joint-most goals (12) in Serie A since the turn of the year, scoring nine and setting up three, level with Juve's Dusan Vlahovic.
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