Hosts Sri Lanka made it two wins out of two ahead of their clash with fancied India in the Under-19 World Cup. Dilhan Cooray's unbeaten 64 helped them to 263-8 off their 50 overs before Namibia were bundled out for 126.
Elsewhere, Nepal - who are in England's group - almost overhauled Zimbabwe's 201, before finishing short on 199-9.
New Zealand piled up 259-6 before Dean Bartlett took 5-30 to skittle Uganda for 137, while Das Neves claimed 5-29 as South Africa beat USA by 162 runs.