It was probably always a big ask for Nonu to adapt to the unique and demanding defensive role of centre against a pacey Crusaders backline given his advancing years – he turns 37 in May – and lack of recent Super Rugby game time after his return from three years in France.
The Crusaders made several important breaks in the midfield during their 24-22 victory and while Nonu wasn't culpable for any obvious missed tackles (in fact he made a very solid one on the sideline which Jordan Taufua might be still feeling), Williams, 33, was when Braydon Ennor burst on to a Ryan Crotty pass.
Nonu and Williams, who played 31 minutes together at Eden Park after Williams replaced Faiane, both have their subtleties but they are also both primarily power players and probably too similar to play alongside each other from the start of a match at least.
Nonu will get his chances this season and his next one could come as soon as the following weekend against the Jaguares in Buenos Aires, but being confined to second-five might not help his push for a return to the All Blacks this year.
"[Nonu] understands the situation around the midfield and how we're going to have to shuffle that midfield around a bit this year to get the best out of him and Sonny," MacDonald added.
"It's important that we use them both well. He understands the big picture. As soon as we told him he wasn't playing this week he said 'well, my first job is to make sure the team prepares well', so that's all we can ask for, really."
The other significant change is Melani Nanai, on the right wing against the Crusaders, starting at fullback ahead of Michael Collins, who made a high-profile error in missing the cross-kick for Manasa Mataele's first try at Eden Park. Caleb Clarke is rewarded for his good pre-season form, including three tries against the Chiefs, with the No14 jersey.
The Blues' All Blacks' props Karl Tu'inukuafe and Ofa Tuungafasi start against the Sharks after their impact role off the bench against the Crusaders – no surprise given the size and physicality of the South African pack – and Dalton Papalii has recovered sufficiently from his hip problem to start at openside flanker.
MacDonald backed 20-year-old replacement first-five Harry Plummer, who has been named on the bench again, to bounce back from his two disappointing late misses off the tee against the Crusaders.
"Harry understands that's the nature of professional sport," MacDonald said. "He would have been disappointed at the time but he's got the skills to be able to park that. He's trained really well this week – he hasn't missed a beat."
Blues team to play the Sharks at Kings Park on Sunday, kick-off 2am NZT, is: 15 Melani Nanai, 14 Caleb Clarke, 13 TJ Faiane, 12 Sonny Bill Williams, 11 Rieko Ioane, 10 Otere Black, 9 Jonathan Ruru; 8 Akira Ioane, 7 Dalton Papalii, 6 Tom Robinson, 5 Josh Goodhue, 4 Patrick Tuipulotu ©, 3 Ofa Tuungafasi, 2 James Parsons, 1 Karl Tu'inukuafe.
Reserves: 16 Matt Moulds, 17 Alex Hodgman, 18 Sione Mafileo, 19 Gerard Cowley-Tuioti, 20 Matt Matich, 21 Augustine Pulu, 22 Harry Plummer, 23 Tanielu Tele'a.