A City side that had opened the scoring in their last 10 matches were left with an unfamiliar feeling when Cash put Aston Villa in front inside the opening 20 minutes.
A short corner was worked to the edge of the box for the Poland international to shift it away from Bernardo Silva and rifle a left-footed shot past an unmoved Gianluigi Donnarumma.
The in-form Erling Haaland looked set to net an immediate equaliser when he raced into the Villa box, but surprisingly, he failed to find a way past Emiliano Martínez.
An injury to Emiliano Buendia cast a shadow on the hosts’ productive first-half display, with his early withdrawal resulting in a first Premier League home appearance for Jadon Sancho in a Villa shirt.
The Manchester United loanee was quickly involved in a move that created the opening for John McGinn to fizz a deflected effort just wide of the target.
Trailing at the break of a league away game for the first time this season, Pep Guardiola’s side made a purposeful start to the second period, with Savinho forcing the Villans to make two last-ditch blocks in quick succession just before the hour mark.
Guardiola turned to his bench to introduce Nico Gonzalez, Nico O'Reilly and Jeremy Doku in a bid to keep the pressure on the Villa backline, however Sancho proved the hosts were not just content with defending their slender advantage, as he wriggled into the box and saw his near-post shot saved before his rebound was also kept out by Donnarumma.
Their failure to add a second briefly looked costly when Haaland slid the ball home in stoppage time, but to Villa’s delight, the assistant’s raised flag effectively confirmed a third consecutive head-to-head home victory.
The statement win moves Villa up to seventh and to within a point of City in fourth, with the visitors also seeing their nine-match unbeaten run across all competitions come to an end.
Flashscore Man of the Match: Matty Cash (Aston Villa)