The Proteas all-rounders were brilliant in this game.
Dickwella missed a direct hit which denied a famous and much-needed win for Sri Lanka.
Owing to his poor run in the series, South Africa might bench Reeza Hendricks.
Lasith Malinga will continue to captain the T20I team in the three-match series as an extension to his limited-overs duty.
The left-hander perished after scoring 94 runs from 70 balls.
Niroshan Dickwella will be Malinga's deputy.
Khawaja replied in style by scoring his 8th Test century.
Southee took a five-wicket haul even as Sri Lanka recovered fro 9/3.
The selectors have picked wicketkeeper-batsman Niroshan Dickwella as Malinga's deputy.
It took only 30 minutes for the visitors to pick the remaining three wickets.