O'Brien cleared to replace Tuffey
O'Brien, 33, will replace Tuffey, who was ruled out of the tournament after breaking his hand while fielding. Tuffey will return to New Zealand for surgery.
O'Brien has featured in 10 ODIs for New Zealand, picking up 14 wickets at 34.85. He last played an ODI against India in Auckland in March this year.
New Zealand, having topped Group B, will play the second-placed team in Group A in the second semi-final at the Wanderers on Saturday.