The former Manchester United striker struck twice to help Uruguay down Bafana Bafana 3-0 last Wednesday and Pienaar said it was very hard to take and that morale in the South Africa camp was very low.
'It's been a very difficult few days since our defeat by Uruguay,' he wrote in his World Cup diary column for the Daily Mail.
'I am still really upset. After the game it was like a funeral in the dressing room. Nobody spoke. No one was in the mood to say what they really felt. In the camp everyone is down.
'The manner of our loss was very frustrating. The first Diego Forlan goal came so quickly that it was as if we had been punched hard in the face.'