Ex-Springboks centre Thinus Delport said South Africa looked "tired and old" as they crashed to the biggest shock defeat in the history of the Rugby World Cup.
Japan deservedly won 34-32 when Karne Hesketh crashed over in the dying moments of timed added on in Brighton, where South Africa had been out-muscled for much of the game and were second best in most facets.
Japan had previously won only one match in their World Cup history - they beat Zimbabwe back in 1991 - and had been restricted to two draws in the 24 years since.
But their momentous win has raised further question marks over Heyneke Meyer's selection, and also the fitness of the Springboks who have a number of their contingent coming back from injury.
"South Africa had too many players coming back from injuries and simply did not look sharp enough," Delport told ESPN.
"They made poor decisions at not going for the points on offer and they generally looked too tired and old.
"It was superb, smart play from Eddie Jones and Japan. They looked much fitter and swarmed the breakdown brilliantly. The brave defence picked off South Africa's one-off runners and the focus on low, chop tackling ensured the Boks never got any real momentum. South Africa gave away too many penalties under pressure."