Bairstow's unbeaten 108 off 48 balls, with eight fours and nine sixes, see Punjab secure the win with eight balls to spare
Eliminated South Africa won the toss on a good batting wicket and took advantage of the conditions to set a challenging target for an Australian side seeking victory to finish top of the round-robin table and set up a semi-final with New Zealand.
Opener Quinton de Kock (52) gave his side a solid start before he became one of two wickets for spinner Nathan Lyon (2-53), but the platform was laid for Du Plessis (100 from 94 balls) and the impressive Rassie van der Dussen (95 from 97 balls).
The pair put on 151 for the third wicket at a run-a-ball, with Van der Dussen making his highest one-day international score before he was caught on the boundary attempting a six off the final ball of the innings to get to his century.