Ouahab (813th in the world) lost 2 sets to 1 (6-4, 2-6, 4-6).
Earlier in the day, Elliot Benchetrit (345th ATP) gave Morocco its first win in the tournament after beating Christian Sigsgaard Petersen (969th in the world) in three sets 7-6, 3-6, 6-2.
Two matches in singles and one in doubles are on the program for the second day, scheduled for Sunday, to determine the winner of this Moroccan/Denmark face-off.
The national team, led by its captain Mehdi Tahiri and which also consists of Adam Moundir and Anas Fattar, hopes to return to Group I of the Davis Cup for a fourth time, after having reached this category in 2001, 2002 and 2004.