Manchester City debutant Marcos Lopes couldn't hide his delight after scoring his first goal for the club against Watford.
Lopes, a Portuguese attacking midfielder who turned 17 only last week.
Mancini, only 16 when he made his Serie A debut, had been planning to give Lopes his debut for some time and the player, a late substitute in the dying minutes, was dumbstruck at his achievement.
He told the club's website: "It was my first game for the first team and my first goal. I have no words to express my feelings.
"I trained on Friday and the coach told me I was in the squad to play but to come on after 86 minutes and score a goal... I have no words to explain it."
Carlos Tevez's rocket of a free-kick which fizzed into the net from 25 yards opened the scoring and Gareth Barry's header just before the break "knocked the stuffing out of Watford", to use City assistant manager David Platt's words.
City's thoughts will now turn to once more trying to rein in league leaders Manchester United. Mancini's men did so last season, and Spanish midfielder David Silva said the target was to cut the gap by the end of February.
Silva said: "It won't be easy but our challenge is to be back level with Manchester United by the end of February.
"Last year we saw how they were in front by quite a lot of points and we won the league anyway, so it can be done." Watford will now concentrate on promotion to the top flight but manager Gianfranco Zola insisted the six changes he made were enforced rather than a case of resting players for the league.
"I believe it was the best team I could put out," he said.
Zola worked with 22-year-old Balotelli and insists the striker can be a "fantastic" player - if his talent can be successfully mastered.
He said: "I have an affection for him. I have worked with him for the under-21s and I do care about him and I do hope his potential is fulfilled.
"It's how to master that potential. I do hope he gets to that position as he will be a fantastic player. I am talking about what he can do to improve his situation but it's not down to me to say how.
"It's just that this is a young man with a lot of potential who can shine."