Lazio were made to pay for a series of missed chances, as Suso’s stunner earned Milan a point at the Olimpico.
The Biancocelesti were dominant, and leading through Lucas Biglia’s penalty, but the Spaniard curled in a late equaliser to prevent an injury-ravaged Diavolo from losing a fourth game in five.
The hosts initially named just one change from the 6-2 win over Pescara, with Stefan Radu replacing Jordan Lukaku at left-back.
However, goalkeeper Federico Marchetti injured his knee in the warm-up, and was replaced by 21-year-old Albanian Tomas Strakosha.
Rossoneri Coach Vincenzo Montella opted to play without a recognised striker, with Gerard Deulofeu operating as a false-nine, flanked by Lucas Ocampos and Suso.
Keita Baldé Diao looked to open the scoring with an early snapshot, but Gigio Donnarumma was equal to it in the Milan goal.
The visitors racked up a series of corners in the opening minutes, but it was the Biancocelesti who could have taken the lead from a set piece.
Radu flicked a corner on, but Ciro Immobile could only spoon it up in the air as he met it at the back post.
The Aquile came even closer just moments later. Lucas Biglia’s half-volley was sweetly struck, but Donnarumma pushed it away, with the 17-year-old also saving the rebound though it would have been offside anyway.
Simone Inzaghi's men were ramping up the pressure, and Immobile headed wide from a Marco Parolo cross, having lost Gustavo Gomez.
The striker was thought he should have had a penalty, but Antonio Damato waved his appeals away after a challenge from Gomez.
The challenge was clumsy, but Immobile went down theatrically when he could perhaps have stayed on his feet and taken a shot at goal.
Immobile was tormenting the Rossoneri backline, and shot wide under pressure from Ignazio Abate.
Wesley Hoedt was next to try his luck, but Donnarumma blocked at close range after the Dutchman had flicked it goalward following Sergej Milinkovic-Savic’s header.
Milan were well and truly under the cosh, but Strakosha was called into action to smother a low shot from Lucas Ocampos.
The Biancocelesti finally made their dominance pay on the stroke of half-time.
Immobile took a fabulous touch in the box, and a combination of Gomez and the onrushing Donnarumma sent the Italian international sprawling to the turf.
The 'keeper was furious about the decision to award the spot kick, but Biglia stepped up to confidently convert from 12 yards.
Replays later showed that Donnarumma hadn’t felled Immobile, but the striker had been sent down by Gomez.
The pattern of play continued in the opening stages of the first half, with Donnarumma bravely collecting a cross from the feet of Milinkovic-Savic and Felipe Anderson smashing one wide.
At the other end, Deulofeu combined with Suso to set up Ocampos, but the winger’s touch was heavy and Vangioni had to intervene to deny Immobile on the break.
Montella had clearly seen enough of the false-nine experiment, sending on Gianluca Lapadula for Ocampos with just over an hour played.
Ignazio Abate thought he should have had a penalty when he was barged over by substitute Senad Lulic.
The Bosnian did appear to have fouled to Rossoneri full-back, but Abate may have been offside in any case.
The visitors were finally coming into the game, and Strakosha was at full stretch to palm away a Jose Sosa free-kick.
Felipe Anderson was giving Vangioni a torrid time down the right, and he smacked a half-volley into the side netting on 76 minutes.
Milinkovic-Savic tried a curling effort, with Donnarumma rooted to the spot and relieved to see it go wide.
It was Donnarumma to the rescue once again as the game entered its final stages, with the Diavolo goalkeeper getting down to save from Immobile after the striker was cleverly played in by Lulic.
The Aquile were made to pay for their profligacy late on, as Suso struck a fantastic equaliser.
Having picked the ball up in the box, the Spaniard managed to create space for himself before curling it into the far corner on his left foot.
Despite having 23 shots, with 10 on target, Inzaghi's side missed the chance to go fourth in Serie A.