A second-half hat-trick from Viktor Gyokeres, along with a goal by Maximiliano Araujo, powered Sporting to a win that left City questioning their form after back-to-back defeats.
Phil Foden put City ahead within just five minutes, capitalising on a mistake from Hidemasa Morita to give the visitors an early edge.
City looked in control as Sporting’s defence initially struggled to contain Foden and Erling Haaland.
However, in the dying moments of the first half, Gyokeres broke through with an equaliser after a superb pass from 17-year-old wing-back Geovany Quenda, giving Sporting a lifeline before the break.
Amorim’s half-time team talk seemed to work wonders as Sporting emerged reinvigorated.
Within seconds of the restart, Araujo struck, giving Sporting a 2-1 lead, while Gyokeres quickly doubled it from the penalty spot after Trincao was brought down by Josko Gvardiol.
City, missing several key players, struggled to contain Sporting’s relentless forward pressure, led by the creative Pedro Goncalves and the trickery of former Wolves winger Trincao.
City’s star striker Haaland had a rare off-night, missing a crucial penalty that could have brought them back into the game.
His strike hit the bar, ending City’s hopes of a comeback. Sporting sealed the win late on, as Gyokeres converted another penalty to complete his hat-trick, following a foul on Geny Catamo.
The win lifts Sporting to second on the group table, while City’s European campaign took a hit, as they dropped to sixth.
With Amorim set to join Manchester United, this memorable night at Estadio Jose Alvalade left an indelible mark on his legacy in Lisbon.
Meanwhile, at Anfield, Liverpool extended their unbeaten Champions League start with a 4-0 rout over Bayer Leverkusen.
Colombian forward Luis Diaz dazzled the home crowd, netting a hat-trick, while Cody Gakpo added a header to complete Liverpool’s dominant second-half display.
Leverkusen, led by former Liverpool star Xabi Alonso, managed to keep Liverpool at bay in the first half, but the Reds erupted after the break, showing their clinical edge.
Liverpool’s impressive form under manager Arne Slot continues, setting up an enticing clash with defending champions Real Madrid in their next group game, while Leverkusen will face RB Salzburg in Germany.