Sideshow Bob on Aguero - Same referee and pre-VAR. It looked for all intents and purposes Alty had no choice but to send him off, and then he appeared to get a message through his headset (touched his finger to his ear), and then... no sending off.
The form Aguero was in at the time, it was a clear a DGSO foul, yet for whatever reason (draw your own conclusions) the officials refused to even entertain it. And remember, this was pre-VAR, so the 4th Official, or whoever spoke to Alty (I have my suspicions) should have had nothing to do with the on-field decision making process.
That decision was the catalyst for both Aguero's and Fernandinho's sending off, and we went on to lose the game.