Green Island also climbed up the ladder with a 2-0 win against FC Twenty11 in a good outing for both Dunedin teams.
The competition is only two weeks old, but the Royals followed up their 3-0 round 1 win against Nomads United with another good result.
Coach Richard Murray suggested the 5-0 margin in Rolleston was flattering for his side.
The game was evenly poised for the opening 80 minutes.
Ben Stanley opened the scoring in the 29th minute from a free kick.
It was cut and thrust with both teams having half-chances before Sean Cooper cut in from the left, beat three or four players and flicked it to Ollie Petersen, who finished from about 15m out in the 82nd minute.
Stanley slotted in a third from a defensive blunder and the game changed complexion when Jak Stevenson was sent off for dissent in the 84th minute.
The Royals banged in two more goals.
Green Island was unable to impose itself on the game as much as it would like in the opening half at Sunnyvale.
The home side adapted its game plan and ended up scoring two nice goals through Harrison McLean in the second half.
The first was a cracker. Keeper Benoit Beaujeon spotted an opportunity. He threw the ball out quickly to Tom Milton, who transferred it to Isaac Hamilton on the left flank.
He played it through to Stefan Milidrag, whose cross found McLean on the penalty spot and he slotted it in.
Beautiful football. Clean, crisp, accurate.
Cameron Anderson made a nifty reverse pass to help set up the second.
Green Island had a 3-0 loss first up against a strong Christchurch United side, but will be pleased with how it has started the campaign.
There were a couple of hat-tricks scored in the opening round of the Southern Premiership.
Nathan Wilke banged in three to help Roslyn Wakari edged the Dunedin City Royals 3-2, and Mosgiel’s Rhys Quarrell grabbed three in a 4-1 win against University.
In the other results, Wanaka beat Northern Hearts 3-1, Northern dispatched Queens Park 4-0 and Queenstown defeated Green Island 2-0.
