The BMW was tracked by a Domino's GPS tracker before it was disabled, court documents stated.
Police spotted the car and pulled it over before arresting the two occupants.
Mr Sharma suffered multiple facial-bone fractures and a cut to the back of the head.
"They did it for fun," he told Hawke's Bay Today after the incident.
He had not known he had been attacked with rocks until police had told him.
"I could have been hit one more time and I would be dead," he said.
Mr Sharma came to Napier last July from his home in Haryana state in northern India to do postgraduate studies in business management at EIT.
He had said he considered himself lucky to have escaped with just upper cheekbone fractures and a gash in the back of the head, and just one night in hospital.
He had found two people in the street who were able to call the police and an ambulance.
Fiti, who faced more charges, pleaded guilty to unlawfully interfering with a vehicle, and possessing a knife in a public place. He was also charged with possessing an offensive weapon but police downgraded the charge yesterday to an additional charge of possessing a knife.
Potaua pleaded guilty to a charge of failing to comply with police when being followed with flashing lights.
Potaua's lawyer Eric Forster told Judge Bridget Mackintosh his client had initially been in custody for three weeks before being granted electronically monitored bail.
He said she had been attending a computing course and had written a letter of apology to Mr Sharma.
Potaua was supported in court by family and a member from the course she was attending.
Fiti's lawyer Matthew Phelps said bail had been declined and his client remained in custody.
Judge Mackintosh made an order for restorative justice to be carried out.
The pair were remanded for sentencing on April 22.
Aggravated robbery carries a maximum penalty of 14 years' jail.
