Nawaf Al Abed scored the only goal of the match in the 68th minute with a vicious shot towards the top corner of the net to beat goalkeeper Elrik Johasen.
Both sides created numerous chances in a cagey opening 25 minutes with Al Hilal looking more sound in quick attacking technique, while the boys in blue squandered several chances in front goal.
No clear-cut chances were created by either side until the 68th minute. Al Abed's powerful shot couldn't be stopped by Johansen's hand but the young City defenders could have done better.
Mancini overhauled his playing XI in the second half giving an opportunity for the reserves who were spearheaded by Kolo Toure. But the young City boys couldn't find a way through their opponents defence.
However, the Saudi giants looked more threatening on the wings, creating two clear goal-scoring chances. But young keeper Johansen made crucial saves as City's defence looked shaky for majority of the second half.
Meanwhile, Sergio Aguero and Edin Dzeko were benched for the opening match as City face tougher oppositions during their training in Austria. City face German side Dynamo Dresden on Tuesday followed by Turkey side Besiktas.
With barely six days into training, City players will come good after a few more days of training while the star players like Samir Nasri, David Silva and Mario Balotelli are yet to return from their summer vacations.