The decision reprieved du Preez, gave South Africa a run, another ball and a free hit and they took the opportunity to clinch a win that crushed India's hopes of reaching the final for the second consecutive tournament.
"I think we can feel sure that the girls have given their all, knowing the importance of the game today," India captain Mithali Raj said. "It was just a good game from both sides. I mean it went to the last ball and it's good for the sport but for the India team it ends our campaign."
South Africa's win also secured a semifinal place for the West Indies who were powerless spectators to the events of the final day. After completing the league matches, they were in third place with seven points behind unbeaten Australia and South Africa who both had qualified.
The West Indies would have been denied a semifinal place if India had won but South Africa's win kept their tournament alive.