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Dhoni was part of the CSK team which selected the players during auctions. Despite widespread criticism that the team is full of 35 plus players, he took no additional step to include fresh blood. There were no replacement for players who became unavailable. When Suresh Raina pulled out (due to some issues with the CSK management), the replacement for him was not available. Even this time, CSK went for players such as Robin Uthappa, who belongs to the 35 plus category.
Not sure whether Dhoni has any say in the auction process when selecting the players, the team management who spends the money and the coaching members will take care of the team selection as far as i know. This time around they rectified all their issues and they were having one of the best seasons with new additions in the team and i was expecting them to dominate this years IPL.
Dhoni is the coolest in all situation. Along with this he have a winning luck with him. This is the reason why we can see more power performance from Chennai and at unexpected situations changing the entire match. Last year this was missing, but the team was criticised for its 35+ player list. In one of the season he played for Pune, by that time he took the team into playoff. So, more than performance he is a lucky player.
I will not call it luck if he is able to take Pune to the play off, from what i have seen he has a much deeper understanding of the game and his intuitions usually works in crucial situations and you can call it luck but i call it his skill set.