The teenage Super Eagle scored twice in the first-half and grabbed a third near the end of a game the Blues dominated from start to finish.
Raheem Sterling capped a fine performance with his tenth goal of the campaign as City continued their quest for a domestic silverware sweep at Villa Park.
With one cup final already guaranteed, City travelled to the Premier League’s bottom club looking to edge a round closer to another Wembley date.
Manuel Pellegrini made four changes from the side that beat Everton in midweek with Yaya Toure rested, Sergio Aguero and David Silva on the bench and Kevin De Bruyne ruled out for several weeks with injury.
That meant Iheanacho had the chance to further showcase his undoubted talents while Bacary Sagna, Fernando and Jesus Navas were also recalled
...Villa 0 City 4...
Though there were vast areas of empty seats inside Villa Park, one end was packed with a partisan, noisy following of nearly 6,000 City fans – and they didn’t have to wait long to celebrate the first goal.
Fabian Delph’s corner was nodded on by Sagna and Fernando’s header was saved by Brad Guzan, but the lurking Iheanacho was quickest to react as he volleyed home from three yards.
It was exactly the start the (ghost green) Blues needed as it immediately took the wind out of a home side already running on fumes confidence-wise.
City had to soak up a few minutes of Villa pressure following the goal, but Villa never troubled Willy Caballero and in truth, didn’t look likely to.
In contrast, the Blues counter-attacked with menace and dominated the midfield battle where Delph, Fernando and Fernandinho eagerly snapped up any loose balls.
A second goal seemed inevitable and it came on 24 minutes via the penalty spot.
Navas scampered down the right before whipping in a low cross towards Sterling, but he was clearly pushed by Bacuna as he raced towards goal.
The infringement was spotted by referee Mike Jones and Iheanacho was calmness personified as he stuttered his run-up and the stroked the ball into the net - Balotelli style.
Even with more than two thirds of the game still to go, the game already looked as good as over
...Villa 0 City 4...
Villa should have been reduced in number not long after the second goal when Bacuna and Sterling had an altercation that ended with Bacuna putting his hands around the City winger’s throat – how he escaped a red card, only the official knows.
Bacuna then bundled Sterling over in another over-zealous challenge moments later and was fortunate that he received a final warning instead of an early bath.
The Blues continued to press forward looking for a third but the teams went into the break without any further scoring.
The host were livelier in the second period, pressing more and having more possession, but the City defence were more than a match for Villa’s probing, and it was the Blues who came closer to adding to their tally with Sterling twice going close in the space of a minute just before the hour-mark.
Villa were finally put out of their misery after 74 minutes when Gana played a back-pass from City’s half and Iheanacho raced clear before finishing clinically as Guzan raced off his line to complete his hat-trick.
It was a stunning achievement by the 19-year-old who now has eight goals from just five starts and within two minutes, he’d assisted City’s fourth as his overhead kick fell to Sterling who bundled the ball home from close range.
There was enough time for Bersant Celina to get another taste of senior football with Angelino and Cameron Humphreys also introduced for their first-team debuts
...Villa 0 City 4...
A terrific display by the Blues who continue to challenge on four fronts going into February.
