"I have full faith in my abilities. All that I can do is control those which can be controlled and I have always done what is required from my side," Zaheer said in Mohali.
The left-arm seamer has been criticised for poor fitness following frequent break down due to injuries last season.
The Baroda paceman, although not at his best, claimed three wickets as Rest of India skittled out Ranji Trophy champs Mumbai for 198 and took a 116-run first innings lead on the second day of the Irani Cup at the PCA Stadium.
Zaheer said playing in the all-India tournaments at the start of the season helped him settle into a rhythm early in the match.
"I felt in good rhythm on Thursday and am getting back to peak form. Playing in the all-India tournaments gave me a chance to bowl 18-20 overs a day.
"I feel things are falling into place," he said.
He said he has made no change in his bowling in response to the hamstring injury that had laid him down twice, in Australia and Pakistan.
"If you see for yourself, my bowling has not changed much. I am doing the same thing that I have been doing before," Zaheer said.
He, however, said that he has been working on his running technique in recent times.
Asked if he should have given himself more time before making his return in July in the Asia Cup where he tore a quadriceps muscle, Zaheer said, "you know that the injury I suffered there (in Sri Lanka) was a different one from the one I suffered before."
When pointed out that skipper Sourav Ganguly had observed after the tournament that he had to work more on his fitness, Zaheer replied, "when injuries happen, naturally the injured has to work more hard on his fitness."