Hendrick Ekstein scored the only goal of the game, nine minutes into the second half, with a smart finish after a slip-up in defence as the ball dropped kindly to him inside the area.

Both sides had started the tie on the front foot and were looking to get forward at every opportunity.

The first real chance fell to the away team as Athini Maqokolo controlled a ball from Langa Mhlongo on the run, only to fire over the crossbar.

There were early calls for a penalty as first Ekstein went down in the Richards Bay box before Nkosikhona Radebe appeared to have been upended by Tlakusani Mthethwa, but on both occasions the referee waved play on.

Thulani Gumede came close to testing goalkeeper Darren Johnson in the AmaZulu goal, but his effort was also narrowly off target.

A Sanele Barns delivery from the right-hand side then caused all sorts of problems for the AmaZulu defence before Johnson ultimately cleared.

Riaan Hanamub then fired into a clutch of bodies as Usuthu broke forward on the half-hour mark, while Thandolwenkosi Ngwenya really should have put his side ahead with a header he sent just off target from an excellent Radebe ball into the box.

Gumede was next to go wide with his header from a central area with 37 minutes on the clock after a swift break forward from the Natal Rich Boys and another good delivery into the box from Barns.

The half, meanwhile, ended with Ian Otieno forced to palm a Keegan Allen free-kick over his goal after the long-range set-piece was allowed to drop inside the area.

Maqokolo was wide with the first chance after the break as AmaZulu made a fast start to the second half, before Otieno made light work of a Hanamub cross from the left with Taariq Fielies lurking.

The away team were playing some probing, passing football but ultimately took the lead after 53 minutes following a mistake in the Bay area.

A ball into the box from the right by Liam Bern fell kindly to Ekstein, who made no mistake with the finish.

AmaZulu had a chance to go two goals up as Ngwenya raced through on goal, but Thembela Sikhakhane got back to make a vital tackle.

There was a tense moment in the Usuthu box as Richards Bay peppered the away defence with a number of deliveries from wide areas, winning several corners that ultimately came to nothing.

Bay were pressing all out for an equaliser, and that was leaving spaces for AmaZulu to exploit.

Otieno made a comfortable save from a Ngwenya shot on the run but then kept his team in the game with a point-blank save off his legs from the same player that should have ended in the back of the net.

There was still a chance for Bay to get back into the tie, and Simphiwe Mcineka thought he had finally hit the target, but Johnson denied what looked a certain goal with a superb save from close range.

Ngwenya has seven goals this season, but he was guilty of the miss of the match — and the chance to kill off the tie — as he side-footed over from in front of the posts from a square Hanamub cross after the Richards Bay defence had been caught napping.

Mutizwa was then off target with a late header before Barns fired over for the last real chance of the tie.

Richards Bay ultimately failed to find a late equaliser to take the tie to extra time. For AmaZulu, they become the first team to secure their place in the last eight of the lucrative competition.

All the other last-8 ties:

Upington City v Durban City
TS Galaxy v Mamelodi Sundowns
Golden Arrows v Stellenbosch
Orlando Pirates v Casric Stars
Milford FC v Mkhambathi
TUKS v Sekhukhune United
Jacksa Spears v Vasco da Gama

Nedbank Cup: Galaxy shock Sundowns as Durban City survive penalty shootout drama