The 32-year-old was given the chance as an opener in Tests and he grabbed it with both hands.
Rohit was unbeaten on 115 when rain intervened.
Here's what he said.
Rohit & Mayank
Rohit and Mayank floor SA on Day 1
Rohit joined hands with Mayank Agarwal (84*) to tame the Proteas attack on Wednesday.
India managed 202/0 in 59.1 overs as rain stopped play.
The two batsmen were cautious at the start and scored freely when the spinners came on.
Both the batsmen played to their strengths and gave India the desired momentum.
Rohit slammed 12 fours and five sixes to show his authority.
Rohit impresses as an opener
This was Rohit's first Test match as an opener of the Indian cricket team. Prior to this, he played 27 Tests and in all these matches, he featured in the middle order. He was promoted as an opener after an inconsistent KL Rahul was dropped.
Rohit grateful to the management, happy he could score runs
Rohit went on to highlight that he wanted to take the opportunity as an opener in Tests and thanked the management for providing him with the same.
"I wanted to take the opportunity and that's why I made the management aware of it. I am grateful to them for providing me with the opportunity and I am happy I could score runs," he said.
I was very clear in my mind, says Rohit
Rohit also said he was clear in his mind.
"I was very clear in my mind what I wanted to do. The new ball will always do a bit in the initial overs -- whether it's red ball or white," he said.
"I have played cricket in India for a long time now and that's why I was aware of the conditions."
'Backing myself and my game was most important for me'
"This was my plan to tackle the new ball and then stick to what I had planned. Backing myself and my game was most important for me because it was all I had in my mind," said Rohit, who slammed many Test records.