The I-League champions, who had drubbed Maldives side Maziya Sports and Recreation 5-2 in their home match in Guwahati last month, scored through Lenny Rodrigues (15th minute), Sony Norde (39th), Cornell Glen (45th) and Jeje Lalpekhlua (82nd) in a Group G match at Mongkok Stadium here.
After their second consecutive at the continental second tier club competition, Mohun Bagan remained on top with six points from two matches, two points clear of Yangon United of Myanmar, who played out a 1-1 draw with Maziya Sports and Recreation in Male, Maldives.
With their head coach Sanjoy Sen at the dug out -- though he was handed a domestic eight-match ban -- the Kolkata side outplayed their opponents at their own den by pumping in three goals in the first half.
Down to 10 men from the 16th minute onwards, South China never recovered and suffered their second consecutive loss. They had lost to Yangon United of Myanmar 1-2 in an away match last month.
The initial minutes saw both the sides trying to gauge each others' strength with Mohun Bagan making some attempts at the South China goal though without much purpose.
Spurred by the home crowd, South China played their
hearts out despite the numerical disadvantage and they got a couple of attempts at the Mohun Bagan goal but Debjit Majumder was upto the task to thwart any danger.
Mohun Bagan gradually took control of the match as Norde scored in the 39th minute to cushion the lead. He intercepted a miss pass from an opposition player, cuts his marker on the left before placing the ball into the far corner of South China net.
With a 3-0 lead and one-man advantage for Mohun Bagan, the match was as good as over by the end of the first half and the visiting side expectedly dominated the second half also.
Glen wasted an easy chance in the 62nd minute as he shot over the bar in front of an open goal after being fed by Lalpekhlua with the goalkeeper out of position.