Montgomery, who will be winning his 98th cap, replaces the impressive Conrad Jantjes at full back, while Pieterson comes in for Odwa Ndungane on the right wing.
"There are certain attributes that the players we've brought in do have and I think we will need them, especially down there," said de Villiers, whose side suffered their first defeat in14 matches last Saturday.
"We are expecting more wet, cold weather and snow down there and we have opted for a left and a right boot in Monty and Butch (James)," De Villiers told Supersport.
"I know that JP is much better in the kicking game than Odwa Ndungane also.
"They know each other, so the communication between the back three should be very good.
"The kicking game is where we lost it last weekend. If we are caught and bogged down in our own 22 we've got enough ammunition to get out of there.
You can watch South Africa continue their build up to the 2009 Lions tour as they take on New Zealand this Saturday at 8.35 am, with the match live on Sky Sports.