The Aussie fly-half will captain the Barbarians in the MasterCard Trophy match against South Africa, but admits he is still smarting from the 35-18 loss.
Giteau said: "It was one of those days. Hopefully next time we will be better prepared."
This week, however, his focus is on taming a South African side who were very physical in a 21-11 win over England last Saturday.
"We have to be prepared for that," he added. "I think they will come with the right attitude and throw the ball around a bit."
Giteau, who has tasted victory for the Barbarians against South Africa and New Zealand in the past, will be partnered at half-back by fellow Aussie Will Genia in a line-up which includes six Australians and five All Blacks, plus Italy's Salvatore Perugini and Wales' Martyn Williams.
South Africa have called up uncapped centre Andries Strauss after Zane Kirchner suffered concussion and an elbow injury against England.
Barbarians: James O'Connor (Aus), Joe Rococoko (Nzl), Drew Mitchell (Aus), Adam Ashley-Cooper (Aus), Ma'a Nonu (Nzl), Matt Giteau (Aus, capt), Will Genia (Aus), Salvatore Perugini (Ita), Stephen Moore (Aus), Neemia Tialata (Nzl), Anton van Zyl (Stormers), Chris Jack (Nzl), Rodney So'oialo (Nzl), Martyn Williams (Wales), Colin Bourke (Chiefs). Substitutes: Keven Mealamu (Nzl), John Yapp (Wales), Quintin Geldenhuys (Ita), Daniel Braid (Nzl), Andy Ellis (Nzl), Stephen Donald (Nzl), Seru Rabini (Fij).