Giteau was selected ahead of Gregan at scrum-half in the recent two-Test series against Wales in Australia, but returned to his more familiar role of inside-centre for the Tri-Nations opener.
The move saw the return of the Gregan, Larkham, Giteau and Mortlock combination, which is likely to form the basis of the Wallabies' World Cup backline.
While Giteau would not be drawn on his own selection aspirations, he believes Gregan's performance against the Boks was good enough to warrant his selection for the upcoming World Cup.
"I think George definitely played well enough to stay at half-back and I think Bernie (Stephen Larkham) and Stirlo (Stirling Mortlock) both played well," Giteau said.
The Wallabies' impressive performance, which saw them hold a 19-10 lead early in the second-half, may have surprised many critics at home and abroad, but Giteau said the team were quietly confident before the match.
"Within the squad we always had that belief that every team is beatable, we still have that belief," he added.
"We came close and we've still got that same belief against the All Blacks."
Giteau agreed that the performance bodes well for Australia's World Cup campaign in September, but admitted the loss was difficult to come to terms with.
"Everyone was pretty shattered, I mean it was the closest I've been, I think, to a win over there, and then to lose the way we did; two good field goals to a replacement player was pretty devastating," he said.Â
"We took a lot out of it, (it's) disappointing, but having said that I think defensively we got a lot out of it.
"We didn't get a real lot of ball in the second half to attack, but when we did get the ball we did show that we can make breaks and make some good yards."