Dissecting his team's narrow and unjust 2-1 defeat on Saturday, the City manager held the thumb and forefinger of his right hand just an inch apart.
'This,' he said, 'is the gap between us now. It is very narrow.' Mancini's disappointment clearly hadn't blanked out his capacity for rational thought. For he was dead right.
The wonder of Wayne: Rooney's scissor kick was a marvellous sight to behold
This superb game of football - a terrific advert for the cut and thrust of the Barclays Premier League - may have been settled by a goal few people in world football could score, but Wayne Rooney's superb bicycle kick will not be all that we remember.
A year after the bitching, sniping and 'Welcome to Manchester' posters, this great city finally has a rivalry to take seriously. Both sides tried to spin it their way after 94 minutes of breathless football at Old Trafford.
Mancini said United were 'not playing well' after Edin Dzeko's shot deflected in off David Silva and levelled things with 25 minutes left. Home manager Sir Alex Ferguson suggested his team had played 'the better football'.
Mind the gap: Mancini knows his side are closing ground on the league leaders
The best defender, meanwhile, was United's Chris Smalling. Drafted in as cover for Rio Ferdinand, he looked born to play in big football matches.
To say the young Englishmanpossesses composure is to understate the matter. From the moment Silvafailed to convert Carlos Tevez's sublime reverse pass in the secondminute - perhaps his only mistake of the game - this could have goneeither way.
Citysaid they were coming to win and they clearly meant it. For a timeafter their equaliser, they looked the more likely winners.
Enlarge We should hear no more about Mancini's 'negative' approach. Here was a real glimpse of what a remarkable force his team are destined to be. As for United, they did what they tend to do these days.
They breathed deeply after Silva's goal, sucked up what City threw at them and broke to score a goal that will be talked about in the same way that people discuss Denis Law's back-heel from 1974.
It was a genuine 'I was there' moment and said everything about United's incredible capacity to deliver when they have to.
Ferguson's team are not the most gifted but are favourites to win a record 19th title simply because they have virtually forgotten how to lose. Mancini spoke in the build up about the importance of a winning mentality. Here was the painful, naked truth of what he meant.
'After our goal I thought we could win,' he said. 'United didn't play well in the second half but some players think if they score they can change a game. This comes when you have been winning things for a long time. We should improve.
'But if we come here and play like this against United then we will be OK. I am very proud of my players. I think we need to win one cup or one title because then we can change the whole mentality of the team.
'I told the players to go home and have a drink. They should be disappointed by the result, not the performance. We are very close to United now, very close.'
Few will forget the derby in September 2009 when a Michael Owen goal won it 4-3 for United. But that said more about City's character than their ability to compete. Saturday's game was different. City are right in United's faces now and are not going to go away.
Former City star Mike Summerbee was laughed out of town for his passionate analysis on Sky. He did, however, have a point. This game served notice of how it will be in the future. They are more than just noisy neighbours now. Wonder goal was for fans. I owed them, admits Man United hero Rooney?400m is not enough! City need to spent more to be champions, insists former chiefAll the latest Manchester City news, features and opinionAll the latest Manchester United news, features and opinion
Explore more:People: Wayne Rooney, Carlos Tevez, Alex Ferguson, Edin Dzeko, Rio Ferdinand, David Silva, Roberto Mancini, Denis Law Places: Manchester