He became the sixth Englishman to gather a ton on test captaincy debut, after Alastair Cook, Kevin Pietersen, Allan Lamb, Andrew Strauss and Archie MacLaren.
The Proteas, meanwhile, rued several missed chances - and an evidently lean seam attack.
With allrounder Chris Morris deemed surplus to requirement in the final XI, captain Dean Elgar ultimately turned to part-time seamers Theunis de Bruyn and Temba Bavuma for five ineffective overs each.
Substitute fielder Aiden Markram, meanwhile, lamented missing a sharp chance given by Root on the fine-leg boundary - and wicketkeeper Quinton de Kock was unable to hold onto an edge afforded by the same batsman.
Fast bowler Morne Morkel, too, afforded allrounder Ben Stokes a reprieve by bowling him, but also literally overstepped the line.
Morkel has now 'taken a wicket' off a no-ball 12 times in international cricket - the most by anyone. Former Australia pace ace Brett Lee did so on 11 occasions.
The reliable Vernon Philander was arguably under-bowled, while pace ace Kagiso Rabada was off key throughout the day - and was guilty of some poor fielding.
Maharaj, well, was largely ineffective - and well targeted by Root and half-centurion Moeen Ali, in particular.
The Proteas' over-rate, too, was sluggish. They should have bowled 90, but fell three short, despite a third session extended by 30 minutes.