Irwandi sustained a bruise in his left eye after the violent incident and was then rushed to the Zainoel Abidin (RSUZA) general hospital for treatment. The incident happened at 3.30 pm, local time, outside the provincial legislative assembly (DPRA) building.
Zaini and Muzakir were sworn in by Home Affairs Minister Gamawan Fauzi at the DPRA building.
The newly installed governor and his deputy will serve the 2012-17 term of office.
The incident occurred at the DPRA building yard, when people attending the inauguration function were leaving the building.
When asked in the hospital, Irwandi said he recognised the person who provoked a group of people to beat him.
"Initially, the person tried to provoke the masses, calling me a traitor. Soon after that, someone hit me from the back, and then another one hit my face, after which my glasses fell and broke," he explained.
"I recognise the provoker and the persons who beat me," Irwandi said, adding that the group also beat up several police personnel who tried to stop them.