Chasing 223 to win, Morgan dealt only in sixes (7) and no fours in the death overs which helped England win the final T20I by five balls eventually in the spirited run-chase. Morgan's fiery knock took him past fifty from just 21st balls, equaling his own record for the fastest T20I fifty for England.
Morgan has now become the fastest man to score a fifty for England in T20s, in just 21 balls.
Besides the outstanding Morgan, opener Jos Buttler (57) and Jonny Bairstow (64), batting at No.3, slammed quick half centuries too after Jason Roy (7) departed early.
England needed 62 runs off 30 balls after Morgan hit Dwaine Pretorius for 14 runs in the 15th over to set the tone. Allrounder Ben Stokes (22) too joined the six-hitting party and his partnership with England's World Cup winning captain, of 61 runs, took the visitors over the line despite Stokes getting out.
Earlier, Heinrich Klaasen hit 66 off 33 balls as South Africa posted 222/6 at SuperSport Park. Klaasen tonked four sixes and four fours just as it had seemed South Africa were falling off the pace after a blistering start between Temba Bavuma (49) and skipper Quinton de Kock (35).
Brief scores: South Africa 222/6 in 20 overs (Heinrich Klaasen 66; Tom Curran 2/33, Ben Stokes 2/35; England 226/5 in 19.1 overs (Jonny Bairstow 64, Eoin Morgan 57 not out, Jos Buttler 57; Lungi Ngidi 2/55
(With agency inputs)