City can move eight points clear of Harry Redknapp's team 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 [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 per cent 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."
Emmanuel Adebayor, who is on a season-long loan from City and will not play this weekend due to the restrictions of the deal, has thrived at White Hart Lane with nine goals, but Mancini has no regrets over letting the £25 million (Dh142m) 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.
Balotelli and the right-back Micah Richards are fit to return for City after ankle and hamstring injuries, respectively.
Redknapp has backed Jermain Defoe to fill the void left by Adebayor's absence. Defoe is becoming increasingly unhappy at his lack of game time this season, but Redknapp has no doubt that the 29-year-old striker will rise to the occasion and combine well with Rafael van der Vaart today.
Redknapp said: "I went to Villa last season and played Defoe and Rafa and we won 2-0. Defoe got sent off that day, but I quite fancy Defoe's movement with Rafa.
"Jermain has been bursting for a chance to get back in and play so he has got the opportunity now.
"We have to play good football in to them, though. We can't be hitting long forward balls up to Defoe expecting him to win challenges with their central defenders."
Wojciech Szczesny, the Arsenal goalkeeper, is determined to make up for picking the ball out of the net eight times at Old Trafford by producing a top display when Manchester United come to the Emirates Stadium today.
”Obviously, I want to make up for what happened at Old Trafford last time around, so I am very excited about the game,” Szczesny told Arsenal Player.
“Somewhere in the back of our heads that game will still be there and we want to make up for it. We just have to focus on our own game, to make sure we are at our best.”
Meanwhile, Wayne Rooney has hailed the winger Antonio Valencia’s return to top form after he struggled with an ankle injury picked up while playing for Ecuador in the Copa America and missed the first month of the season.
“Antonio has been playing brilliantly,” said the United striker.
“It is great for the forwards because he is so good at delivering the ball into the box quickly.”