The hosts took the lead in the 11th minute and successfully protected their advantage for the remainder of the match. Despite DR Congo enjoying more possession and creating several opportunities, they were unable to find an equaliser.
Mauritania defended resolutely and limited the visitors to few clear-cut chances. The result gives the West African side a slender advantage heading into the return fixture.
DR Congo will need to overturn the one-goal deficit when the second leg takes place on 6 October in Lubumbashi. A home win by any margin would see the Congolese side progress, while a draw would favour Mauritania on away goals under the current qualifying format.
Both teams will now prepare for the decisive return match as they continue their bids to reach the U23 AFCON finals. The narrow scoreline leaves the tie finely balanced and sets up an intriguing second leg in the Democratic Republic of Congo.