The initial squad contained only ten players with previous Lions experience - including Derek Quinnell, Andy Irvine and Fran Cotton - but Millar called on eight more players to cover for the nine who were forced to drop out.
Two of them would never play international rugby again - Stuart Lane suffered a knee injury and Rodney O'Donnell damaged his neck and was forced to retire.
And despite winning all of their non-international matches under the coaching of Noel Murphy, the Lions got off to a morale-sapping start in Cape Town.
Graham Price touched down for the tourists while five penalties and a drop goal by Tony Ward were also in vain as South Africa ran in five tries - Willie du Plessis, Gerrie Germishuys, Rob Louw, Divan Serfontein, Moaner van Heerden all crossing.
The Lions went on to lose the next two Tests, in Bloemfontein and Port Elizabeth respectably, but they were not to be denied the taste of victory.
They travelled to Pretoria looking to avoid only the second-ever Lions whitewash and captain Bill Beaumont led from the front.
The Lions earned some reward for their first-half dominance when Clive Williams found his way to the South African line, before du Plessis responded just after the break.
It was a familiar tale for the tourists - in the third Test they had led 7-3 at the break only to be denied - but this time it was different.
In three spectacular minutes the game was turned on its head, Irvine and John O'Driscoll turning what looked like a fourth straight defeat into a 17-13 victory - despite Ollie Campbell missing a couple of conversions.
"A lot of boys out there today put on the old red shirt for the last time," said Lions hooker Peter Wheeler afterwards. "I'm happy for them.
"I'm also happy for Ollie Campbell. He is the best kicker of a ball from the ground I have ever seen, and it would have been tragic for him if we'd lost the Test because he hadn't kicked his goals."