The 27-year-old opened his side scoring after converting a penalty in the 28th minute to level the scores after Becir Omeragic’s own-goal gave St. Gallen the lead in the 7th minute.
Blaz Kramer and Lindrit Kamberi’s goals in the 78th and 86th minutes were enough to seal the winner for FC Zurich.
Scorpions’ goal-poacher, Assan Ceesay has now scored 11 goals for FC Zurich with the latest coinciding with his 100th game in the Swiss First Division League.
Gambia all-time leading goal scorer, Ceesay played 100 games in the Swiss Super League between two clubs (Lugano and FC Zurich).
He helped his side go seven games unbeaten, winning their last six games in a row.
The victory extended Zurich lead at the top with 40 points, pending Basel game against Grasshopper.
Assan Ceesay moved to Switzerland when he signed for FC Lugano from Senegalese side Casa Sports in 2016. He later moved on-loaned to FC Chiasso in 2017 before going to FC Zurich in 2018.