The teams meet at HP Oval on Tuesday, October 27, with the series level at 1-1.
Ireland scored 229 for nine, then bowled Namibia out for 174 in Windhoek.
The Ireland captain hit 56 off 71 balls, while Carmichael added 45 off 80.
Namibia posted 321 for six, then bowled Ireland out for 290 to win by 31 runs.
The Namibia captain hit 14 fours and four sixes in 125 balls, a career-best score.
Frylinck scored 76 off 90 balls as the pair passed 100 runs together.
Jack Brassell took four for 52, removing Stirling, Tucker, Campher and Dockrell.
It was Namibia's first ever ODI win over a Full Member nation, the leading tier.
Stirling hit 77 off 71 balls, with Campher adding 45 and Dockrell 48.
Two games will remain after Tuesday in the five-match series.
Erasmus has 156 not out behind him, while Stirling has scores of 56 and 77.
Read the full explainer, both games so far, and what happens next.
Get the full breakdown, key numbers, and what happens next.
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