Sri Lanka's faltering campaign suffered a fresh blow as Nuwan Pradeep was ruled out for the remainder of the tournament.
Sri Lanka made two changes, Australia one on Saturday in London.
Sri Lanka have not played a match since June 4; Australia are without Marcus Stoinis.
Sri Lanka will take a call on his availability for the match with Australia on Friday.
Pradeep had put his right hand up to protect his face from a straight shot hit back at him and injured himself in the process.
Afghanistan, playing in only their second World Cup, beat Sri Lanka soundly in last year's Asia Cup in the United Arab Emirates, but for the second match in a row this World Cup their batting let them down.
Chasing a revised target of 187 after the rain interrupted the proceedings, Afghanistan were all out for 152.
Aggressive half-centuries from captain Faf du Plessis and opener Hashim Amla before late fireworks from Chris Morris powered South Africa to 338/7.
Sri Lanka begin their World Cup campaign against New Zealand on June 1 in Cardiff.
Sri Lanka have suffered another major injury setback with right-arm pacer Lahiru Kumara being ruled out of their ongoing Australia tour.