With the scores level at one goal apiece, Adelaide captain Ryan Kitto downed Abel Walatee in the 59th minute of Saturday's match at Coopers Stadium.
Kitto did not appear to challenge the ball when he denied Walatee a clear opportunity at goal and the Reds went on to secure victory via Zach Clough.
Carl Veart's men could finish as high as third on the table this round, after two wins and one draw to start the A-League Men season.
But Western United (0-2-2) remain winless, leaving Aloisi feeling bitter about the non-penalty decision.
The former Socceroo said he would be sending a 'please explain' to the league over the matter.
"I haven't seen anything as clear that's not awarded a penalty," Aloisi said.
"I'm disappointed that (the referee) didn't see it, then I'm disappointed that the VAR didn't see it.
"Even the opposition players said that they can't believe that wasn't a penalty.Â
"Definitely a 'please explain' (but) it's not going to change anything, because it killed the game."
Walatee looks to be taken down in the box...but no penalty is given �— Paramount+ Australia (@ParamountPlusAU) It's starting to heat up here at Coopers, as both sides hunt for the go-ahead goal#ADLvWUN is live on Paramount+ 📺 pic.twitter.com/f58iHsdp2JNovember 9, 2024
Kitto had opened the door for the visitors to draw first blood in the 10th minute when he fouled Riku Danzaki, giving away a free-kick outside the box.
United centre-back Dylan Leonard's pass towards goal bounced between players before Kane Vidmar snuck it past the Adelaide defence to cap the set piece.
But their dominance did not last long.
With off-season recruit Dylan Pierias as the spark, Clough pulled off a cutback to teenager Luka Jovanovic.
Jovanovic sent the goal just wide but the ball deflected off 17-year-old Leonard into goal in the 32nd minute.
Vidmar cleared the ball but his desperate act was too late, with a VAR check confirming the Western United own goal.
Talk about a game of inches �😲 After VAR review, — Isuzu UTE A-League (@aleaguemen) @AdelaideUnited draw level by the finest of margins!Seriously unlucky for 17-year-old defender Dylan Leonard, but the Reds won't care!Watch #ADLvWUN live NOW on Paramount+ and 10 Bold 📺 pic.twitter.com/aXr0HmPVwlNovember 9, 2024
Englishman Clough finally hit the scoreboard in the 71st minute when he received a clever pass from Jonny Yull deep in the box.
"Even though we weren't at the level that we want to be at, we still created some very good moments," Veart said.
"It just shows the desire in this group this year. It's a very strong group that want to achieve something."
Former Reds sharpshooter Hiroshi Ibusuki momentarily stole the show when he was greeted with an accidental punch to the face by keeper James Delianov.
Moving to Western United in the offseason, Ibusuki was looking to make a header when Delianov - who had eyes on the ball - charged forward to clear the threat with his fist.
Ibusuki, who was already sporting tape near his left eye, shook off concussion concerns and Aloisi later confirmed he was cleared of injury.