Since losing by a single point to England at Twickenham in their tour opener, the Springboks have managed to beat France in Paris and Scotland in Edinburgh in their subsequent Tests.
Speaking in the Welsh capital on Monday afternoon, Erasmus was very clear on the challenge that awaits his Springbok side on Saturday.
“In our view, Wales are definitely the most difficult opponent we will face on this tour,” emphasised Erasmus.
“Warren (Gatland) has managed to build a superb side, with lots of experience and they are playing a good, balanced game, plus they have good depth and quality in their squad.
“They put Tonga away last weekend and the previous week they defeated Australia, so we are preparing ourselves for the most difficult Test of this tour.”
Meanwhile, World Rugby announced that Springbok captain Siya Kolisi has received a Citing Commissioner Warning for an incident that happened in the 31st minute of the Test against Scotland on Saturday at BT Murrayfield.
Erasmus said it was a good thing to know the outcome so early in the week: “He’s our captain and to have him available from the beginning of the week is good because sometimes these things can take a while as they look for clarity.”
The Springboks started their preparation with a field session on Monday afternoon, and they will do so again on Tuesday and Thursday, when Erasmus will confirm the Springbok match-23.