In head-to-head contests, the Sri Lankans have lost 16 of their last 18 one-day internationals against South Africa, including the last five, but are growing in confidence on the back of performances from veterans Lasith Malinga and Angelo Mathews.
South Africa is already out of contention after winning just one of its first seven games at the tournament. Two Sri Lanka's six competition points come from washed out games earlier in the tournament.
The weather forecast for Durham is for a cloudy start, clearing to sunny in the afternoon.
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