A win to the Island would have moved coach Malcolm Fleming's side ahead of Roslyn, but in the 90th minute, Roslyn substitute Damo Foster grabbed a goal to seal a 2-2 draw.
Neither side played to its potential and as many thrills were generated by mistakes as by creative play, but there were plenty of express breaks and robust tackles to keep referee Edward Cook on his toes.
Green Island scored first after 30 minutes when Sean McIntee hit his fourth goal in as many games. Roslyn replied within minutes as Isaac Nicholson equalised with a well taken strike.
Both sides made chances, and found space with direct quick breaks on the wings, but good goalkeeping by Josh Dijkstra (Green Island) and Tom Stevens (Roslyn) looked likely to deny more goals.
However, in the 84th minute, Ben Kiore found space in Roslyn's goalmouth and nodded in a rare header that looked like a match winner.
But in the remaining minutes, Cam Attwood pushed forward, Curtis Day made some deft passes and eventually a left wing cross found super sub Foster lurking, and he made no mistake with a first time shot that at last beat Dijkstra in goal.
Goals looked unlikely at the Caledonian Ground, where Northern blunted Mosgiel initially and some pedestrian build ups by the Plainsmen were absorbed with relative ease.
In contrast, Northern spent its lesser ball possession on longer passing to big Angus Milne, with keen support from David Henderson and Greg Thurlow, and centreback Jack Rea pushing forward.
Chilean Eder Franchini's excellent technique broke the deadlock with a superbly hit freekick to beat Northern keeper Freddie Haidekker. Then, from midfield, Rahan Ali made the score 2 0 at halftime.
Cody Brook chested down a cross from Franchini and hit the net, and Matt Kelly, back from injury, rounded a defender and slipped in the fourth and final goal.
It was business as usual at Tonga Park, where Caversham notched a 7-0 win over University to stretch its lead at the top of the competition table to 13 points, with just two games left to play.
Second placed Dunedin Technical, on a bye this week, has 31 points and still has five games to play. Theoretically, it could catch Caversham.
But Caversham's classy form and prodigious goal scoring suggests that another FPL title is on its way to the trophy shelf.
Coach Tim Horner's side has lifted its scoring average to more than five goals a game.
It was Andrew Ridden's turn this week to hit a hat trick, but inevitably the Jackson brothers, Tom and Lewis, joined in, as did Sam Collier and Jude Fitzpatrick.
