Visiting captain Temba Bavuma called heads, but the coin came down as tails for Rahul to celebrate with a fist bump as India's curse of a million-to-one ended in Visakhapatnam.
It was more than two years since India won the toss in a one-day match.
The crowd roared and a smiling Rahul elected to bowl in the deciding third match of the series, which is level at 1-1.
India's players were quick to congratulate Rahul, who is leading the ODI team in place of the injured Shubman Gill.
Rahul credited presenter Murali Kartik for his presence as a lucky charm as India won their first ODI toss since the World Cup semi-final in Mumbai against New Zealand on November 15th, 2023.
"You should do more tosses for us," a beaming Rahul said.
Former India batter Sanjay Bangar said Rahul's ploy of flipping the coin with his left hand instead of the usual right did the trick.