It will take City winning a first league title since 1968 to convince the Italian otherwise even if Sunday's thrashing of their more decorated rivals had counterpart Sir Alex Ferguson bemoaning "the worst result in my history."
"This is only one game," Mancini told a news conference. "I think United is one yard above us still... we can change this only if we win [the title] in the end. After maybe it is different but now United is better than us."
Mancini's men inflicted a first Old Trafford defeat on their hosts for 18 months, making a mockery of the glittering home record that formed the backbone of last season's record 19th league title.
Two goals apiece from Mario Balotelli and Edin Dzeko, as well as strikes from David Silva and Sergio Aguero, sent City on their way to a famous win as one of the most keenly awaited Manchester derbies in years lived up to its billing.
City have now scored a massive 33 goals in nine league games as this season's more attacking approach has paid off.
Three of their strikers - Aguero, Dzeko and Balotelli - are among the league's top five scorers and all owe much to the creative panache of fleet-footed Silva whose vision and distribution are at the heart of so many City chances.
Mancini was full of admiration for United's attempts to attack despite being down to 10 men for most of the second half following Jonny Evans' dismissal - the very approach that angered Ferguson.
"At times our full-backs were almost our wingers and we were playing almost two versus three at the back. That was suicide and crazy," Ferguson said on the club website.
"We just kept attacking. It's alright playing with the history books but common sense has to come in at times. With the experience we had at the back, we should have realised that and settled for what we had when it went to 4-1."
Ferguson was adamant the heavy defeat, which came after something of a lacklustre month following a blistering start to their title defence, would galvanise his team.
"That kind of defeat will make an impact on the players," he said. "There's a lot of embarrassment in the dressing room and quite rightly so. Hopefully they'll show that [reaction] next week."
Mancini said the thumping was unlikely to knock United's confidence too much and emphasised that this was merely one win regardless of the number of goals.
"I think the season will be very long, probably there will be four or five teams who can win the title," said Mancini, who led City to their first major trophy in 35 years with victory in the FA Cup last season.
"It's important for our confidence, it's important because we showed we are a good team.
"United are too strong for this [letting it get to them]. They know like me that it is only three points."
City lead the way with 25 points, with United five behind and third-placed Chelsea on 19 after the Londoners slipped up themselves in a 1-0 defeat at Queens Park Rang
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