ETIHAD STADIUM - MANCHESTER
Watford completely dominated the first-half, with Giuseppe Sannino's tactics bamboozling the Blues and causing them all sorts of problems. They had runners in every area of the pitch, and goals from Fernando Forestieri and the excellent Troy Deeney gave them an unlikely but thoroughly deserved half-time lead.
Pellegrini responded with a tactical shakeup of his own, and City began to improve. Aguero's hat-trick and a long-range strike from Aleksandar Kolarov ensured City progression to the fifth round.
Here we look back at the major talking points from City's FA Cup scare.