Top-order batter Dewald Brevis struck 75, but could not prevent South Africa suffering a surprise 18-run defeat by hosts Namibia in the opening match of a Twenty20 tri-series.
After losing the toss in Windhoek, Namibia posted 163-9 thanks mainly to openers Jan Frylinck (60) and Louren Steenkamp (40).
The reply from experimental South Africa began badly with openers Lhuan-dre Pretorius (9) and Jordan Hermann (7) going cheaply.
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With Brevis at the wicket there was hope, but when he fell to the final ball of the 17th over, getting a thick outside edge to a full toss, the die was cast and South Africa ended on 145-9.
Namibia are a second-tier cricket nation and 17th in the world T20I rankings, 12 places below South Africa, who face Zimbabwe on Saturday in the second of six mini-league matches.
South Africa, Zimbabwe and Namibia will co-host the 2027 ODI Cricket World Cup from October 4 to November 21.