In a strong start by Roslyn, Luke Clissold nearly scored with a bicycle kick, only to see Morgan Day head it clear off the line.
With 12 minutes gone, Cam Anderson swung in a corner which Roslyn goalkeeper Tom Stevens punched powerfully away. However, it landed at the feet of Morgan Day, who from 25m out found the back of the net.
Roslyn's wide men Victor Pekkari and Reid Hulleman were a constant menace. Hulleman shot just wide on the 28-minute mark, before Pekkari forced a smart save from Levi Waddington moments later.
A robust challenge by Mosgiel's Day on 40 minutes was adjudged to have been in the box and a penalty was awarded.
Roslyn Ollie Colloty - who had already scored two penalties this year - confidentially stepped up but Waddington was up to the task, getting down low to push the shot away.
The early stages of the second half were a bit scrappy until the 63rd minute, when Roslyn gave away possession to Aiden Barbour-Ryan, who took the ball forward, turned his defender and drove his shot into the bottom left corner.
Roslyn rallied and when Colloty swung in a corner, Kasam Alis' beautifully timed shot cannoned off the cross bar. Another Colloty corner on 71 minutes was bundled over the line by Nathan Wilkie and despite the linesman raising his flag, the goal was given.
Mosgiel's Liam Dungey restored the two-goal buffer with a well placed header following a corner with 15 minutes left.
Then Rory Findlay launched a long clearance and found Cam Anderson, who with a deft touch toed it past the onrushing Stevens to make it 4-1 to Mosgiel.
With time nearly up, Roslyn's Hulleman was denied a deserved goal by a fantastic one-handed save from Waddington.
In the clash between the third and fourth placed teams at the Queenstown Events Centre, Queenstown started brightly but lost Liam Gould to injury after 10 minutes. University, playing 4-3-3, took a deserved lead on 38 minutes when Allan McBride made it 1-0.
Queenstown's Zac Hourston worked tirelessly and equalised in the 45th minute, cutting in from the left to unleash a low drive into the bottom corner.
In time added on, Hourston was awarded a penalty following a handball decision and Carlos Hermann sent keeper Stu Catto the wrong way.
Straight from the restart Queenstown won a free kick 25m out, and Hermann bent the ball over the wall to make it 3-1.
In a dominant first-half display, Southland scored three unanswered goals against Northern, from David Mwangi, Davi de Carvalho and Liam McClure.
Ben Rea made the final score 4-0 when he scored in the 58th minute.
The game between Caversham and Green Island at Sunnyvale was abandoned with three minutes to go after Green Island's Matt Milton suffered a sickening leg break.
The game was evenly poised at that stage 1-1.
Caversham went ahead inside the first minute with a penalty. Green Island goalkeeper Christian Firth saved the initial kick, but the linesman flagged for it to be retaken and on the second attempt Caversham scored .
Caversham held the lead into the second half but was unable to stop Max Johnson from equalising with a header, following a cross from Genta Kojima.
With three minutes to go, Milton was fouled in the penalty box and Green Island was awarded a penalty. However, due to the seriousness of Milton's injury and the delay, referee Calvin Berg decided to abandon the game.
In another result, Technical beat Wanaka 3-0.
-By Neville Watson
