Huck's victory was not unanimous, with two favouring the Serbian-born fighter (117-111, 115-113) and the other scoring it level (114-114).
Huck rocked the Londoner - who had 'Kryptonite' written on his waistband - in the fourth then Afolabi came back to finish strongly, landing a few hard blows, but it was not enough.
Huck, 28, improves to 36-2-1 (25 KOs) in making the 11th defence of his title while Los Angeles-based boxer Afolabi, 33, is now 19-3-4 (9 KOs).
It was the third confrontation between the two men: Huck won the first on points in 2009 and the rematch in 2012 ended in a draw.
Early last year Huck fought WBA heavyweight champion Alexander Povetkin of Russia but lost on points.
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