One of the ironies of the Springboks' current mix-and-match selection strategy and the consequent iffy nature of their recent performances is that, if they could replicate the ease with which the centre combinations have gelled, there wouldn't be this headache.Jesse Kriel's fine showing in the past weekend's narrow 22-21 victory over Argentina at Ellis Park was indicative of the good form all of Jacques Nienaber's specialist midfielders are boasting.Despite a petulant, deliberate knock-down souring his evening, Damian de Allende - Kriel's positional partner - also improved markedly from his misfire in Auckland a fortnight ago, while Andre Esterhuizen delivered his best performance in a Bok jersey alongside a composed, if somewhat muted, Lukhanyo Am against the Wallabies at Loftus.Naturally, it's a testament to the four men's temperaments ahead of the World Cup in France, but also the overlooked fact that the majority of the respective combinations between the men are well established.De Allende and Am, South Africa's 2019 title-winning combo in Japan, remain the team's first-choice duo, but the match against the Pumas was a vivid reminder that before they established their rapport, De Allende and Kriel were long-term partners in crime, so to speak.The two men had been one of the few highlights of the Boks' 2015 World Cup campaign under Heyneke Meyer in showcasing maturity beyond their years and were even still touted as Rassie Erasmus' go-to pair in 2018, when they starred together in a narrow loss to the All Blacks at Loftus.Meanwhile, Esterhuizen and Am's dovetail against the Wallabies shouldn't have been surprising to discerning viewers, who would've known they were South Africa's most influential centre pairing in