Even with Sergio Aguero rested, Balotelli was left on the bench following his training ground bust-up with manager Roberto Mancini. It was left to Tevez, the source of such controversy at the club last season, and a goal on his debut by teenage Portuguese midfielder Marcos Lopes to put the smile back on Mancini's face.
Lopes, nicknamed 'Rony' after the Brazilian forward Ronaldinho, only turned 17 last week and struck the third in injury time after Gareth Barry had made in 2-0 just before the break.
Tevez was straight into the action, carving out an easy chance for Edin Dzeko, who was wearing gloves despite a mild afternoon in Manchester, and he fluffed his effort.
The pressure on Watford was unrelenting though and when City took the lead in the 25th minute the visitors had barely strayed into their opponents' half, let alone had a shot.
City had already had a Dzeko goal ruled out for offside when Tevez was crudely felled 25 yards out by Watford skipper John Eustace. Tevez ran up and drilled the free-kick with immense power, the ball still rising as it hit the back of the net with keeper Jonathan Bond clutching at thin air.
Almost immediately afterwards, Watford had - and spurned - their best chance of the match. An excellent passage of one-touch passing saw Fernando Forestieri, one of the many Udinese players on loan at Watford, through one-on-one with City's keeper Costel Pantilimon but the Romanian pulled off an excellent diving save low to his left.
It was 2-0 a minute before half-time as City sliced through Watford's defence again. David Silva's ball to James Milner created the space and his cross was easy for Barry to head firmly past Bond.
Then came Balotelli's chance to make amends. As he waited to come on in the technical area next to Mancini, the Watford fans chanted 'fight fight fight' but he nearly scored with his first touch, cutting inside and leashing a powerful shot that was well saved and Tevez stabbed the rebound wide.
With three minutes left Mancini gave a debut to Lopes and it turned into one of the dream variety - the teenager pouncing to fire home in injury time after Bond had only managed to parry Balotelli's low drive.