They were returning home from Christchurch about 3pm when the Mazda car, driven by the 77-year-old man, drifted across the road on to the northbound lane and into the right-hand verge, hitting a road sign opposite Dunstan Downs, Constable Craig Bennett, of Kurow, said.
It then appeared the man, who said he had been feeling tired, over-corrected the car.
It rotated, hit a bank and then rotated again and slammed into the bank.
The car was extensively damaged and the couple, who received minor injuries, had a "very lucky escape", Const Bennett said.
It was another reminder for motorists to take care over the holiday period, particularly if they were feeling tired, he said.