Playing in fantastic conditions at Tahuna Park on Saturday, the Royals took an eighth-minute lead when Sam Caldwell drove to the goal line and squared the ball across for Gabriel Varrica to side-foot home from close range.
Mosgiel responded when Harvey Stephens linked with Patrick Koppert, who shot narrowly wide.
The Royals had a great opportunity to make it 2-0 in the 19th minute when Varrica crossed the ball with Connor Neil waiting at the far post.
But he glanced his header off target and Mosgiel nearly made them pay three minutes later.
Matt Adye sped past his marker and drilled in a cross which was deflected goalward and it took a goal line clearance to keep it out.
On the half-hour mark the game was end-to-end with chances for both sides — a Mosgiel corner was cleared, but only to the edge of the box, and Luke Clissold’s well-executed goal-bound volley was blocked.
The Royals then broke as Ashton Hodson burst into the penalty box, only to be denied by a well-timed tackle from George Duncan.
Mosgiel’s next attack resulted in a corner delivered by Stephens and Koppert’s acrobatic scissor kick was cleared off the line.
As the first half came to a close, the Royals threatened with first Kazik Swain crossing from the left to Cato Williams, who headed narrowly wide, then Hodson had a powerfully struck shot well-saved by keeper Dan Robinson.
With time up Mosgiel switched off and were dispossessed in the middle of the park.
The Royals countered, Hodson timing his run to perfection to sweep the ball home for a 2-0 lead.
But he wasn’t finished. In first-half injury time, Varrica nodded the ball back across the goal for Hodson to pounce from point blank range to score a brace and make the game safe for the Royals.
The Royals looked to extend their lead in the opening period of the second half with Neil, Swain and Hodson all having shooting opportunities. Swain having quite an influence in midfield dictating the play and he did make it 4-0 in the 53rd minute, when a well-worked corner found him at the edge of the box and he drilled a low shot past Robinson.
It was 5-0 when substitute Fraser Anderson, in the penalty box, had time to look up and pick his man in the 63rd minute. He passed to Neil, whose well-struck shot found the back of the net.
Mosgiel got a consolation goal when Ryan Walker jinked his way into the Royals penalty box and his bending shot was palmed away by keeper Alex Boomer into the path of debutant Campbell Thompson with six minutes left.
The Royals are joined in the last 16 of the cup by Northern, who beat University 2-1, with first half goals to Toby Orchiston and Janic Gorman, before Henry Pierce pulled one back for the students in the last couple of minutes.
Cashmere Tech overcame Ferrymead Bays 4-3, with Lyle Matthysen getting the winner in the 83rd minute, while Nelson Suburbs beat Nomads United 2-0.
In the Kate Sheppard Cup, the Dunedin City Royals beat Otago University 2-0, avenging their loss to the students a year ago.
Hannah Mackay-Wright opened the scoring for the Royals in the fifth minute, before Kylie Jones scored in the 52nd minute to give them breathing room.
They will move on to face Cashmere Technical in the quarterfinals, the Christchurch team having beaten Nelson Suburbs 10-0 after nine first-half goals. — Neville Watson
