The game got off to a slow start, with the amount of goal-mouth chances few and far between from both sides.
Bucks were looking to become the first second-tier side in this year’s competition to take the scalp of a Premiership side, and did pose a few prudent questions to their more fancied hosts.
Angelo Kerspuy’s well-taken free-kick 14 minutes before half time found the head of Mashale Rantabane, who headed wide of goal.
As a result, the first half ended goalless, but the display towards the closing stages by Usuthu, indicated a sign of things to come from them in the second stanza.
Instead, the NFD side broke the deadlock albeit deservedly through the head of Rantabane, who made amends for his earlier indiscretion to profit from Siyabonga Dubula’s delivery in the 56th minute.
Buoyed by the lead, Bucks were confident of an upset but they were pegged back by Togolese Sadate Ouro-Akoriko who latched home from Tapelo Nyongo’s assist after 64 minutes.
Derby hero Siyethemba Mnguni found acres of space inside the box and tested the ability of Olivier Kwizera, who rose to the occasion with an expertly tipped save later on.
Usuthu brought on veteran Mabhuti Khenyeza for Camaldine Abraw in the closing stages with extra-time fast approaching.
The game went into extra time after both sides could not be separated, and Usuthu didn’t take long to go in front through Simphiwe Lunkwana in the opening minute after a good cross by Kheli Dube.
Duncan Lechesa’s side tried to conjure up an immediate reply through Kaketso Majadibodu, but his effort was saved by Baolefa Pule.
Rantabane though got his brace to force the game into a penalty shootout with the equaliser on the stroke of full time.
The penalty sequence saw the hosts reign supreme and join Bidvest Wits and Ubuntu Cape Town in the last 16.
AmaZulu: Pule, Sikhakhane, Mabiliso, Nyongo, Ouro-Akoriko, Mnguni, Darpoh, Ncube, Ncobeni (Lumkwana 90'), Dlamini (Ramphele 81'), Abraw (Khenyeza 81').
Subs: Mbatha, Mthembu, Dlamini, Lumkwana, Maduna, Ramphele, Khenyeza.
Bucks: Kwizera, Majadibou, Ndletyana, Rantabane, Letsisa, Ntuli, Kerspuy (Bhengu 95'), Dubula (Fukutwa 75'), Japhta (Kangwa 101'), Uhuru, Erasmus.
Subs: Nkala, Mashego, Leonard, Bhengu, Khumalo, Fukutwa, Kangwa.