Ponting, who has been struggling for runs in the tournament, had to sit out in order to accommodate fellow countryman and pacer Mitchell Johnson in the squad.
Specifying that it was Ponting's personal decision to step down, Sharma said, "It takes a lot of heart and guts to do that. We felt that we wanted to get the right combination and he was the one who stood up and said 'I would not be playing this game'."
"I felt really good when the management handed me the responsibility. I was little nervous initially as I was leading the side for the first time. But the nervousness went off after entering the field. I wanted to concentrate on what I need to do. I am very happy with the way I approached."
Having registered a fine victory under difficult conditions at the Eden Gardens, Sharma said: "It was our third away game on the trot. We have been playing good at home so we wanted to win as many away games as possible. This is one of them.
Mumbai Indians struggled in the middle after losing the wickets of Dwayne Smith and Kieron Pollard, before Harbhajan Singh calmed the nerves with a six in the last over.