The Boks were by far the dominant team in the first half of both matches -- albeit not on the scoreboard -- but somehow they contrived to lose them by two points and one respectively.
In the match against New Zealand, Erasmus was criticised for emptying his bench too early and taking off key players in a tight encounter. Erasmus said afterwards that players such as scrumhalf Faf de Klerk, who was substituted for the first time in the Rugby Championship at Loftus Versfeld, were struggling with cramp.
After the match against England, Erasmus came in for a lot of stick for not making changes sooner in the match, especially after the Boks' lineout struggles earlier in the encounter.
The fact is the Springboks couldn't close out another big Test, never mind Owen Farrell's no-arms tackle on Andre Esterhuizen, that should have resulted in a penalty for the Boks. They let another famous result slip through their fingers. It's something -- with the Rugby World Cup less than a year away -- that could leave psychological scars.
How and when the Springboks use their bench has become a big issue. The timing of substitutions seems to have more to do with fatigue than tactics. There seems to be no plan in terms of the makeup of the bench, and it seems as if players 16 to 23 are selected simply to fit into the team rather than a game plan.
Players such as De Klerk and hooker Malcolm Marx are very important for the Boks, and it's probably fair to say that Erasmus wants them on the field for the majority of a Test match. But both players have played a ton of minutes in positions where it's rather difficult to play beyond 65 minutes.
Both players also tend to play really deep, because they contribute a lot on the field. Both have been nominated for the World Rugby's Player of the Year award, befitting their performances, and their importance to the Boks, but unfortunately the players behind them haven't had a lot of minutes to enhance their reputations.
Marx had his worst Test of the year on Saturday, missing his jumpers on a couple of key occasions when the Boks were on attack five metres from the home team's line. However, he still played past the 70th minute, despite having an off day.
Hooker Bongi Mbonambi was superb at in the home series against England, finding his jumpers and playing a massive role around the park. Yet he started only one match in the Rugby Championship, against Australia away, and was taken off after 35 minutes "because of fatigue". Marx was fit again, and Mbonambi basically played only a bit-part role off the bench.
Talented scrumhalf Embrose Papier was the Boks' cover at No 9 in five of their Rugby Championship fixtures, but he made it off the bench in only two of those matches; he went on at wing against Argentina in Durban, before taking over from De Klerk against the All Blacks in Pretoria with less than 10 minutes to go.
But what sort of impact can players such as Mbonambi and Papier -- or anyone -- be expected to make with less than 10 minutes to go in a fixture?
Former Boks coach Peter de Villiers made the point the other day that the All Blacks rarely leave their subs on the bench past the 70-minute mark.
The All Blacks' use of their bench is two-fold -- to make an impact and to expose inexperienced players to the rigours of Test rugby. De Villiers said the All Blacks were ruthless in the last 20 minutes of Test matches, and seemingly had another gear, because their players had enough time off the bench to adjust to the pace of the game.
Erasmus tends to change his props quite early, especially on the loosehead side where Steven Kitshoff has provided a lot of fire and a proper impact off the bench. Would Kitshoff have the same influence on the game with just five or six minutes to go? Probably not.
South Africa managed to keep the All Blacks at bay in Wellington through sheer guts and determination, while the home side also made uncharacteristic mistakes in the final quarter of the match. But in Pretoria, the All Blacks' bench came on to the field and helped the team score three tries in the last 18 minutes.
The Boks' replacements, who took the field 10 minutes after their All Blacks' counterparts, couldn't manage that intensity in the final 10 minutes. A young player such as Papier also didn't get enough minutes earlier in the campaign to adapt to the situation on the field as well.
Rugby has become a 23-man game, but South Africa are still stuck with looking at the 15 best players and then trying to replicate that on the bench -- instead of looking at replacements who can complement the starters and fit into a strategy for the final quarter.
Erasmus' World Cup starting team is taking shape, but he also needs to build a bench that can close out tight matches or win a fixture when the starters aren't quite firing.
That requires a change of mindset, and soon, especially as the Boks coach has only seven more Tests before the World Cup opener against the All Blacks. Because, on the evidence of the past two Test matches, 23 players win you a Test, and not just the starting 15.