Cameroon were beaten 1-0 by the DR Congo on Sunday as they launched a bid to win the All Africa Games football title a record fourth consecutive time.
Mutombo Kazadi scored the only goal in Kinshasa midway through the second half of this final round, first leg qualifier.
The winners after the return match on 9 July in Yaounde will join seven others at the finals in Mozambique in September.
Cameroon had travelled to Kinshasa without defender Jean-Patrick Ndzana after he was dropped for indiscipline.
They were hoping to get back on the winning trail after a shock recent Olympic Games loss to Tanzania.
All Africa Games and Olympic Games qualifiers are restricted to under-23 footballers.
Cameroon won the African competition in 1999 (Johannesburg), 2003 (Abuja) and 2007 (Algiers).
Meanwhile, Uganda all but booked their place in Mozambique after humiliating neighbours Kenya 5-1 in Nairobi on Monday.
The match was scheduled for Sunday but was abandoned after heavy rain made the Nyayo National Stadium unfit for play.
Uganda drew first blood in the 30th minute through Hamisi Kiiza but Musa Ateya equalised five minutes later.
Uganda's other four goals arrived in the second. Kiiza Hamisi scored twice while Habibu Kavuma and Emma Okwii contributed one each.