Steve David Heimuli Tonga, 31, pleaded guilty to assaults occasioning bodily harm in public, while adversely affected by an intoxicating substance.
Prosecutor Harriet Hearn said Tonga had been drinking at 237 Flinders St and had approached a man at the bar at 11.40pm on April 25.
The man turned around and Tonga punched him in the left side of his jaw.
As the man fell to the ground Tonga tried to land a second punch, but missed.
While the man was on the floor, he held his hands over his face as Tonga punched him again.
