O'Driscoll watched from the sidelines as Ireland allowed a nine-point lead to slip after a spirited comeback from the Springboks.
The Leinster centre thinks that Ireland got complacent after the break and were ultimately made to pay.
He told BBC Sport: "We soaked up too much pressure, allowing them to come at us. You can't sit back on a lead against South Africa.
"They had that pressure in the second half and probably deserved their victory."
The 33-year-old has been forced out of Ireland's autumn series after undergoing surgery on an injured ankle last month.