Jefferson scored his fifth goal in his last six matches to help Sliema Wanderers back into fourth place alongside Floriana and keep St Andrews second from bottom at the other end of the table.
The Wanderers were quickest into their stride at the start of the second half. Substitute Michele Sansone, who came on for Peter Xuereb, was given time to pick out Jefferson who buried a low drive at the far post via the woodwork.
Fourteen minutes from time, Ricardo Correa swung in a cross which Gavric met at the far post to hit the back of the net with an impressive header- as the fight finally went out of St Andrews.