South Antrim always looked the better team but it was late in the game when they stamped their authority on the South Antrim League Premier Division game at the Recreation centre.
Belvoir made a good start and took the lead through Ronan Wright, but Stephen McNeice levelled for South before half-time in a keenly contested game.
Belvoir had lost their centre-half through injury earlier but they held on till the latter stages of the match.
Francis McCrudden finally gave South the lead before McNeice added his own second goal.
Belvoir had a player sent-off during this period and with no substitutes finished the game with nine-men.
Karl McCartney popped in a fourth goal for South to give them a well-deserved win.
Belvoir manager, Neil McConnell, said they had to send players with the seconds, who were short, and this left the firsts with a bare minimum.
“We coped well under the circumstances, but need more players available on Saturdays.’’
South boss, Darren Downes, said he was pleased with the performance, but thought the Ironside Cup semi-final, which is looming, has been in their minds too much.