The Indian coach feels Rahane's innings was the turning point in the Boxing Day Test.
Rahane produced a brilliant knock of 112 which helped India take a crucial 131-run lead in the first innings. The visitors then bowled out the hosts for 200 in their second essay and then chased down the 70-run target comfortably.
"I think, it was the innings of Ajinkya Rahane. The discipline, you know on such a big stage...When he (Rahane) went out to bat, we were 2 down for 60, and then to bat six hours, on probably the toughest day to bat, because it was overcast all day and he batted for six hours, unbelievable concentration," Shastri said at the post-match virtual press conference, as quoted by PTI.
"I thought that was the turning point. His innings was the turning point," he added.
Rahane also earned from the coach for his shrewd captaincy while handling the resources at his disposal.
"He is a very shrewd leader and a good reader of the game. I thought his calm composure out there helped the debutants as well as the bowlers. There was a calming influence out there inspite of losing Umesh," Shastri remarked.
The India coach was also asked about the difference in captaincy style of Rahane and Kohli, who left the Australian shores after the series opener in Adelaide for the birth of his first child.
"See, both are good readers of the game, Virat is very passionate, Ajinkya, on the other hand, is very calm and composed, and it's their characters.
"Virat is more in your face while Ajinkya is quite prepared to sit back in a very calm and composed manner, but deep inside he knows what he wants," he opined.
India had suffered a humiliating 8-wicket defeat in the opening Test. With this victory, they levelled the series 1-1, with two Tests still to be played in the Border-Gavaskar Trophy.
(With PTI inputs)