A second-wicket partnership of 125 runs between Root and Alex Hales frustrated the Proteas bowling attack before Kagiso Rabada finally made the breakthrough in the 27th over.
Before Hales carelessly gave away his wicket it seemed as though run outs would be the only way to make a dent to the English batting lineup.
England opener Jason Roy (20) was the victim of some poor running between the wickets when taking the second run was caught short of the crease with Proteas wicketkeeper Quinton de Kock removing the bails.
Roy’s departure brought Root and Hales together for their century stand which lasted just over 20 overs before Rabada struck twice in the 27th over.
Hales knock of top edged Rabada’s short delivery to fine leg where Morkel took the catch on the rope to send the opener to the changeroom on 65 runs from 73 runs with England on 161/2.
Rabada struck again two deliveries later to remove Jos Buttler on a duck with JP Duminy taking a superb catch at short-square leg.
Eoin Morgan’s (8) stay at the crease also proved to be a short one facing 24 balls before David Wiese claimed his wicket with Hashim Amla taking the catch at short midwicket with England on 187/4.
South Africa seemed to be making inroads at this point but the partnership between Root and the new man at the crease, Ben Stokes, brought on a run fest.
The duo combined for a fifth wicket partnership of 82 runs from only 54 deliveries before Root was finally run out.
At this stage the damage had been done with three more wickets falling before the end of the innings with the tale adding 49 runs in the remaining seven overs.
Independent MediaJoe Root batted to his highest ODI score of 125 runs to lead his side to competitive 318/8 in the third ODI at SuperSport Park.
Original source: Root has Proteas in a panic