The Barclays Premier League leaders host the Londoners in an eagerly-anticipated clash at the Etihad Stadium. City, who thrashed Spurs 5-1 when the sides met at White Hart Lane in August, can move eight points clear of Harry Redknapp's men by completing a league double.
"I think when you play against a top squad like Tottenham, (Manchester) United or Chelsea and you win it, your mentality improves. Your feeling is better, your confidence is better. I think that is very important, like when we beat Arsenal at home," said Mancini.
"It is not easy to recover eight points if they (Spurs) lose, but everything can happen. We maybe didn't think United could lose at home to Blackburn or at Newcastle. So, for this reason, if you don't take every game 100% it is difficult."
Redknapp has taken a swipe at City ahead of the clash by referring to the huge amount of money invested in the club since their Abu Dhabi-led takeover in 2008. However, City had finished ninth the previous season and Mancini believes the club could only quickly become title challengers by spending heavily.
He feels the situation was different for the other clubs - even though they have paid out some large fees anyway - because they already had players to sustain higher league positions.
Mancini said: "All people say this, he (Redknapp) is not the first. For Tottenham, Man United it is different because when you always play at the top you can maybe change only two or three players per year.
"Now the difference is every time City goes to buy one player that costs maybe eight or nine million, when City arrive there, (the price) is ?20million.
"But if you have a chance to spend, buy good players if you can. I think they [Tottenham] have bought good players. Maybe not in two years like us, but in the last 10 years they have bought good players and spent money like all the teams.
"We have good players but Tottenham are the same - Van der Vaart, Bale, Gallas, Kaboul, Lennon, Adebayor, Modric - and I don't think they are young players without experience. For this reason they can win the title."