Marquee striker Marc Janko scored twice for Sydney, which was winless in seven A-League matches and goalless in four before the AFC Asian Cup break.
But with French-born Senegalese cousins Mickael Tavares and Jacques Faty making their debut for Sydney in Graham Arnold's first match back at Gosford as an opposition coach, the Sky Blues burst to life against a lacklustre Mariners in front of a crowd of 12,102 in round 15.
Janko started the rout in the 16th minute when he was left unmarked to bring down a cross from Alex Gersbach and finish with his left foot.
The Austrian captain's goal was the first for Sydney in six and a half hours of A-League action stretching back to a 3-3 draw with Melbourne Victory in round 10.
The visitor made it 2-0 just two minutes later when an unmarked Chris Naumoff scored his first A-League goal, sweetly hitting a left-foot strike off a cross from Aaron Calver.
Bernie Ibini, who had a shot knocked wide by Liam Reddy in the 29th minute, made it 3-0 in the 44th when given time and space to take a ball through from Alex Brosque and score.
There was no respite after the break as Janko was gifted his second goal in the 48th minute when he pounced on Zac Anderson's limp back-pass to knock the ball past an advancing Reddy.
The host finally had reason to celebrate when Josh Rose took the ball 80 metres in the 66th minute before drawing keeper Vedran Janjetovic and giving debutant substitute Travis Major an open goal to make it 4-1.
However, Sydney ended any chance of a comeback in the 72nd minute when Ibini played Janko into space and the Austrian cut back a ball for Brosque to steer it home.
The result lifted fifth-placed Sydney to 22 points.
