Rabat Ajax failed to close in on leaders Zejtun Corinthians as an early goal condemned them to a fifth 0-1 defeat.
Peter Xuereb scored the all-important goal for San Gwann after just three minutes.
Birzebbuga St. Peter’s join the Magpies on 30 points after a 2-1 win over Mgarr United. Ronnie Celeste put the Saints ahead, Ishmael Cutajar levelled matters but Paul Camilleri notched the winner for Birzebbuga.
In another match, St. Patrick returned to winning ways as they beat Gzira United 3-1 thanks to a brace by Glenn Barry and a goal by Gordon Failla. Josef Felice scored a consolation goal for the Maroons.
Naxxar Lions defeated Senglea Athletic 4-0 in another match thanks to a hat-trick by Darren Falzon and a goal by Adrian Fenech.
Zejtun lead the way with 36 points, followed by Mellieha and Naxxar on 32, Rabat and Birzebbuga 30, St. Patrick 26, San Gwann 19, Senglea, Gzira and Zebbug 18, Zurrieq 16 and Mgarr 7.