South African coach Mickey Arthur laid into his players after New Zealand cruised to victory in the second one-day international on Friday.
New Zealand won by seven wickets with 11.2 overs to spare to level the series ahead of the decider in Cape Town on Sunday.
The result ended a run of five victories by South Africa.
"We were poor in all three departments, this has been our worst game in a long while," Arthur told a news conference.
"We were very ordinary and our dressing room is very disappointed. We've rocked up at every game and expected to roll them over.
"The New Zealand dressing room is more hungry than ours at the moment and that's a concern. They did it all right tonight and we did it all poorly."
New Zealand captain Daniel Vettori, by contrast, was full of praise for his team.
"It was a complete performance, you couldn't ask more of the team," Vettori said. "It was a very good one-day victory."
South Africa squeaked to a two-wicket win off the last ball in the first match of the series in Durban on Sunday, a result that was still fresh in the New Zealanders' minds.
"The first words out of a lot of the guys' mouths were that we should have won in Durban, so the series should be over now," Vettori said.
"But that's not the way it is. Now that we've got the momentum we've got to make sure we hold onto it."
South Africa may have to take on the buoyant New Zealanders in Cape Town without captain Graeme Smith, who has been laid low by a virus.