The day-night game at the Premadasa stadium will hold only academic interest as Sri Lanka gained an unassailable 3-1 lead following their eight-wicket win in Pallekele on Sunday.
South African captain AB de Villiers said he wants a win to improve his nation's poor track record in Sri Lanka, where the Proteas have won just two of their 14 completed one-dayers going back to 1993.
"There is a lot to gain from the last game," de Villiers said. "We have not won much in Sri Lanka, so we are very keen to finish on a high.
"Besides, every match that you play for South Africa is an important one, regardless of the state of the series."
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The skipper laid the blame for the series loss on poor batting on spin-friendly pitches.
"What we need are a few 100s and some good partnerships," said de Villiers. "The bowlers have been playing good cricket, but we as batsmen have just not supported them well enough.
"This is a chance to show what we are capable of with the bat. Every player in the squad takes pride in his performance and they will no doubt want to finish the series successfully.