A strong second half performance helped the Blitzboks advance to yet another Cup semi-final after they overturned a half-time deficit to defeat New Zealand.
New Zealand held a slender 12-7 half-time lead but two converted tries in a period of dominance by the South Africans saw them grab a healthy 21-12 lead before conceding a late try.
They will now go up against the United States, who defeated England 27-7, in the Cup semi-final.
In the other quarter-finals, a strong second half performance helped Australia advance to the Cup semi-final when they defeated Argentina. Australia will face Fiji in the next round after the Pacific Islanders put Canada to the sword in the second half.
In the Challenge trophy, Scotland scored a late to edge out Samoa, France put the hammer down in the second half to edge out Wales, South Korea were no match for Russia and Kenya did enough to squeak out victory.
Scotland will play France and Russia will go up against Kenya to see who will contest the Challenge Cup Final.
South Africa 21-19 New Zealand
South Africa got off to the perfect start as Dylan Sage ripped the ball away fro their opponents. The Series leaders maintained possession before flinging it out wide to Chris Dry, who muscled his way over. Branco du Preez added the extras to ensure a 7-0 lead.
NZ maintained possession for the remainder of the half and found reward in the sixth minute when they dotted down in the corner after sustained pressure on the Blitzboks to trail 5-7. Sage was then shown yellow soon after to hand New Zealand the one-man advantage.
South Africa attempted a late attack but a loose pass was plucked out of the air and the Kiwis raced away from the halfway line to dot down and claim a 12-7 lead at the break.
The Blitzboks were back in the lead soon after the restart when Cecil Afrika showed his speed as he sliced through New Zealand's defence to dot down. Du Preez added the conversion to take a 14-12 lead.
South Africa continued to pile the pressure on New Zealand's defence as the game wore on and it paid off in the 13th minute when, after a sustained attack, Werner Kok dotted down from close range. Afrika added the extras as South Africa took an unassailable lead.
New Zealand looked for a final hoorah in the final play of the game and grabbed the last points of the game when they dotted down in the corner, while Zain Davids was sent to the bin in the lead-up.
USA 27-7 England
England came out firing and opened the scoring in the opening minute with a converted effort before the United States closed out the half in command. An unconverted fourth-minute try saw them trail 5- before a second unconverted score ensured a 10-7 lead. There was enough time for one final try in the half as the USA took a 15-7 half-time lead.
The United States remained in control of the game as an early unconverted second half try stretched their lead to 20-7 as England struggled to get themselves in the game. England pushed hard to get something from the second half but an intercept try in the final play helped the USA advance.
Fiji 29-12 Canada
It was a tense first half as the sides took the game to their opponents. Fiji opened the scoring in the first minute with an unconverted try, only for Canada to hit back in the fourth minute with an unconverted effort of their own. Canada then took the lead compliments of a converted effort before Fiji levelled matters at 12-12 in the final play of the half.
There was no stopping Fiji in the second half though as two tries, one converted, early in the second stanza ensured a 24-12 lead. There was time for one more unconverted try as Fiji marched on to yet another semi-final.
Australia 21-12 Argentina
Argentina were the first on the board in the third minute with a converted try but Australia dotted down in the closing stages of the half to head into the break level at 7-7.
Australia found their groove in the second half and scored a further two converted tries by the 12th minute to take a commanding 21-7 lead. Argentina had the final say of the game though as they grabbed a late unconverted try.
Challenge Trophy quarter-finals
Samoa 21-26 Scotland
Scotland got the scoring going in the opening minute with a converted try, only for Samoa to hit back with two converted tries of their own to take a 14-7 lead in the fifth minute. Scotland hit back just before the break to level the score at 14-14.
The Scots took the lead early in the second half, only for Samoa to edge their noses ahead 21-19 in the 14th minute. The final play of the game lasted two minutes and it was enough for Scotland to grab the match winning converted try.
Wales 21-28 France
France opened the scoring in the opening minute with a converted try but Wales bounced back to level it up. France went into the break with a 14-7 lead though after they scored a late converted try.
Wales were back on level terms early in the second half but France stepped up their intensity soon after as they dotted down two quick seven pointers that ensured a 28-14 lead with a minute left to play. Wales had the final say of the game though as they bagged a late converted score.
Russia 43-0 South Korea
Russia wee in an unforgiving mood and took a commanding 22-0 lead at half-time, thanks to three unconverted tries in the opening six minutes and a further converted effort with the final play of the half.
The second half remained all Russia as three converted tries rounded up the victory.
Kenya 24-17 Japan
Japan were reduced to six men early in the encounter and Kenya took full advantage to open the scoring with a converted try. But Japan closed out the half strongly as they dotted down twice, with a solitary conversion, to take a 12-7 lead at the break.
Kenya regained the lead early, 19-12, in the second half through two scores, one converted, before being reduced to sis men on the field. Japan managed a solitary unconverted try in that time to narrow the deficit to 17-19 but Kenya had enough in the tank for a final try, despite having a second player in the sin bin.
Semi-final fixtures: (Kick-off is local time - GMT plus eight hours)
Samoa v Wales (13.14)
South Korea v Japan (13.36)
Scotland v France (13.58)
Russia v Kenya (14.22)
Argentina v Canada (14.47)
England v New Zealand (15:09)
Australia v Fiji (15.31)
USA v South Africa(15.53
For more rugby news, visit Rugby365.com