Du Plessis, who announced earlier on Monday that he was stepping down from the captaincy, is part of a 16-man squad to be captained by Quinton de Kock.
South Africa won the toss at the Wanderers Stadium, asked Sri Lanka to bat and bowled them out for 231, a total the hosts overtook with more than 11 overs to spare
Hashim Amla was not included for the start of South Africa’s last series before the Cricket World Cup in England from May to July - but selection convener Linda Zondi said Amla, 35, remained a senior player.