The upset win on Saturday came against a patchwork South Africa side, with most of their top T20 players on duty in Pakistan.
But it still didn't take any shine off their remarkable four-wicket win in the one-off Twenty20.
Zane Green, who scored 30 not out, struck a boundary off the last delivery of the match to seal a famous victory for the hosts.
South Africa had won the toss and elected to bat but wickets fell regularly as they limped to 8-134, Jason Smith top-scoring with 31.
Namibia left-arm seamer Ruben Trumpelmann completed impressive figures of 3-28.
Namibia, who have qualified for next year's T20 World Cup in India and Sri Lanka, then battled to 6-138 in reply.
The match had marked the return to the South Africa side of swashbuckling opener Quinton de Kock, after the 32-year-old changed his mind about retirement.
But his first international knock in 16 months lasted only four balls as he was dismissed in the first over for one.
De Kock is in South Africa's squad for a three-match T20 series and three one-day internationals in Pakistan this month.
