David Wagner's men thought they had won it when Kachunga rifled home and video replays suggested the effort may have been wrongly disallowed.
One player who is expected to play is Vincent Kompany, the City skipper having missed the last two matches through injury.
But he is unlikely to play a part against Watford.
The onus, though, will be on summer signings of Andre Gray, Richarlison and Andre Carrillo to attack a City defence that has looked vulnerable despite not conceding a single goal post the global break.
We are backing Jesus as our prediction in this market, and you can get the best odds for him at Unibet. He was so important last season.
The Portugal midfielder has been used sparingly since his £43million summer move from Monaco by manager Pep Guardiola.
Roy Hodgson's first match in charge of Crystal Palace looked like the team's previous four matches.
"Last season we weren't able to win many games against the top five or six in the Premier League and we didn't win away in the Champions League".
Watford have been playing catch up for just 33 minutes in the Premier League this season.
When it comes to Premier League bogey teams, Manchester City appear to be one for Watford, with Portuguese boss Marco Silva hoping his side can overturn those bad fortunes this weekend.
Even if Aguero was modest, his teammates summed up his brilliance with Ilkay Gundogan calling him a "goal machine" and his last goal "incredible" while Raheem Sterling put it perfectly: "Give Sergio Aguero a chance and nine times out of 10 he'll score".
The other unbeaten team so far are City's rivals Manchester United, who host Everton tomorrow on Wayne Rooney's return to Old Trafford. Forwards Gabriel Jesus and Sergio Aguero are developing a genuine partnership and they seem to be meshing well. However, we are backing a 3-1 win for the Citizens as our prediction in this game.