Reigning champions Australia have already qualified for the semi-finals, while South Africa cannot make it through to the last four.
South Africa need just one good performance to turn it around says JP Duminy as the side gears up to take on "big threat" India.
Will Amla make the cut? Has Markram done enough? With will replace Ngidi? Who is Tahir's spin partner?
JP Duminy, who scored 76 runs in the series, has jumped from 39th to 32nd spot.
Reeza Hendricks made 66, his second straight half-century, and captain JP Duminy hit 34 not out off 14 deliveries as South Africa finished the innings strongly.
Sri Lankan captain Lasith Malinga said he hoped his side could restrict South Africa to "150 or 160" and then put on a better batting performance than they have managed in losing all five one-day internationals as well as the first two T20 games.
Sri Lanka will hope for a consolation win after having already surrendered the T20I series.
Hendricks and Van der Dussen put on 116 off 78 balls for South Africa's second wicket.
Sri Lanka, meanwhile, will be eager to break 6-match losing streak in the limited-overs series on this tour.
Faf du Plessis and Quinton de Kock will be rested for the second and third T20Is of the series.