Possibly, but if it was a real issue the first place you'd expect to see it is in defence and against both the Boks and NZ we only conceded 10 in the second half - which we'd probably have taken before kick off.
Against Aus we conceded 22 in the second half, but still scored 19 so it's not like we were totally out on our knees.
That we didn't score after the 60th minute NZ or 52nd v Aus is hugely disappointing. Fatigue may have contributed to some mistakes, but for me it's a peripheral factor to several others.