The Spaniard, who formerly held the same role at Barcelona, joined City last weekend, with the club announcing his role would include supporting Mancini in player recruitment. But the City boss expects Begiristain to fulfil the same role football administrator Brian Marwood has in previous transfer windows of completing the deals once targets have been identified.
Mancini said: "I want to decide which players we take, this is normal for every manager. I worked with Brian for three years, he was sporting director, I think Txiki will do the same job. I have my job and Txiki will have his job. I don't want to go to talk with other teams to buy players, this is not my job. Like every sporting director, he will talk with me before buying players."
Mancini is now working alongside two former Barcelona men in Begiristain and chief executive Ferran Soriano, but he shrugged off speculation ex-Barca manager Pep Guardiola could follow.
Mancini said of Begiristain: "I am very happy. He has a lot of experience with a top club like Barca. If we did well in the last two years, I think we can do better in the future.
"If people write that Txiki is here and maybe next year Guardiola will arrive or another manager, this is not my problem. I'm here, I want to continue to work well because I think we are ready to improve and build a stronger team."
City closed to within one point of Barclays Premier League leaders Chelsea with last weekend's win over Swansea and on Saturday they take on West Ham at Upton Park.
The match comes only three days before their Champions League clash against Ajax, which City must win to keep their slim hopes of qualification for the knockout stages alive.
But Mancini insists their minds will be solely on West Ham, particularly given the threat of Andy Carroll. The striker is yet to score this season but he did find the net against City for both Newcastle and Liverpool two seasons ago.
Mancini said: "We need to think only about West Ham because tomorrow will be a tough game, a very physical game and if we don't play very strong it will be difficult. Andy Carroll causes a lot of problems for every team because he's a strong player and usually at home it's very difficult to mark him. We need to play very strong as a team."
Source: PA
Source: PA