Mark Stewart doubled the lead on the stroke of half time, finishing off a well-worked set-piece.
Stewart scored his second and South's third with a delightful left-footed free-kick.
Mikey Sparkes rounded off the scoring, much to the delight of manager Marks.
He told JC Sport: "I said after our defeat last week that we were still the team to beat and I was delighted with the way we bounced back under difficult circumstances.
"We currently have seven first-teamers out injured and it is brilliant to see we have strength in depth as we embark on a tough five weeks.
"It was also fantastic to see young Ethan Krell make his debut at the age of 16 for the first team."