Rohit Sharma labelled his maiden Test double century as "probably the most challenging" innings he has played.

India took complete control of the third and final Test against South Africa on day two in Ranchi, with Rohit scoring 212 from 225 deliveries to help the hosts to 497-9 declared, the Proteas reaching stumps on 9-2 in reply.

Rohit, who had three double hundreds in ODIs but never in the five-day format, faced a nervy wait after lunch was called while he was on 199.

The 32-year-old, who has excelled at the top of the order having endured a stop-start Test career to date, then saw out a maiden over upon resumption before finally getting over the line with an excellent pull for six off Lungi Ngidi. 

Asked about his wait, Rohit said: "That's the nature of the game. You can't do anything about it. I wouldn't say it's frustrating. It's just the laws of the game. 

"The time [a session] has to finish, it has to finish on that time.

"From my side, I wasn't thinking about that at all. Because I knew the time will come and whenever it's supposed to happen, it will happen. I was just trying to be positive, think positive at that particular time. 

"I know it can be frustrating at times but there's nothing you can do about it. I just went back happy [at lunch], you know, 199 not out, I'd take that any day."

Rohit now has six centuries in Test cricket but conceded this was the toughest innings he has played.

"I haven't played much, I have played only 30 Test matches," he added. 

"Yes, in terms of what was thrown at me in this particular Test match, I would definitely say that it was probably the most challenging one."

India had stumbled to 39-3 on day one before Rohit was joined by Ajinkya Rahane, with the duo putting on an outstanding fourth-wicket stand of 267.

"We've seen Ajinkya for so many years, the way his Test career has progressed, and whenever the team has been in a difficult situation, he's come and rescued us," Rohit said. 

"This isn't something he's done just once or twice, he's done it in many innings. This shows how strong he is, mentally, and how much hunger he has, to be able to steer the team out of bad situations.

"We've seen it outside India, we've seen it in India as well, so Ajinkya's Test graph, it's climbing one step at a time, and there can't be anything better for the team, because if your middle order is strong, whatever situation comes, you're confident that one guy will always put his hand up and take the team forward."