Jadeja took five for 33 in his nine-over spell as South Africa were skittled for 83 and the hosts marched to an eighth win out of eight matches in the tournament.
It was the first time in the tournament that India, who made 326-5 in their innings, had won the toss and chosen to bat.
"After winning the toss, we were trying to challenge ourselves," Jadeja told reporters.
"It was a challenge for us to bat first because in the second innings, if the dew comes, we needed to figure out how to bowl with the dew.
"If such a situation comes in the knockout stage, we should know how to handle that situation.
"In white ball cricket, sometimes due to the dew factor, conditions can change completely," he added.
Despite South Africa's paltry tally, Jadeja thought pitch conditions for the batsmen had been tougher earlier in the day when India were at the crease.
"If you ask me personally, the wicket in the evening was a little easier. I won't say easy, but it was fine," he said.
"But in the afternoon, there was turn and it was slow, so batsmen can't hit. But credit to Virat (Kohli) and the middle order batsmen who handled their spinners, it was very good."
Kohli's unbeaten 101 off 121 balls was the backbone of India's innings as he scored his 49th one-day international century on his 35th birthday, matching Sachin Tendulkar's record.
"I would say this is special for him," Jadeja said.
"Very few people get a chance to wear the Indian jersey so it is a big thing. But if you have a good performance on your birthday and the team wins, then it becomes doubly special."
India have already qualified for the semi-finals ahead of their final group-stage match against the Netherlands in Bangalore on Thursday.
"The way the team's momentum is right now, with batting, bowling, in every department, we are clicking as a team," Jadeja said.
"We will continue and try to make it the same in the semi-final and final."
