The 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.
Mancini said: "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.
"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."
City and Spurs are growing accustomed to playing each other for high stakes.
In each of the last two years they have met late in the season with a place in the Champions League on the line.
In 2010, Spurs prevailed to snatch fourth place in the Premier League, but City turned the tables last year and went on to finish third while the Londoners had to settle for the Europa League.
Mancini said: "It is now three years we have played against Tottenham in an important game. This says us and Tottenham are good teams, we are always there.
"This year is different because we are playing for the title and I think this is a good thing for us and Tottenham."
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."
Emmanuel Adebayor is actually on a season-long loan from City and will not play this weekend due to the restrictions of the deal.
Adebayor has thrived at White Hart Lane with nine goals, but Mancini has no regrets over letting the £25million man leave, having been satisfied with the goal output of
Sergio Aguero, Edin Dzeko and Mario Balotelli.
He said: "We have good strikers, we have scored a lot of goals until now and we did well."
City have dipped from their free-scoring form of earlier in the campaign with league defeats to Chelsea and Sunderland followed by consecutive cup losses to Manchester United and Liverpool.
They got back to winning ways at Wigan on Monday, but only by a narrow 1-0 scoreline.
City still have two games to play without their suspended captain Vincent Kompany, while Kolo and Yaya Toure are away at the African Nations Cup.
Mancini said: "Wigan was important but we have had four or five games in this situation. We can have difficulties, like against Wigan.
"We deserved to win because we had the chances to score the second goal, but I think every game is difficult in this moment."
