Madrid turned in a fine performance to defeat Barcelona at Camp Nou last time out, but Carlo Ancelotti's side lacked any spark on Thursday.
It is the third successive home game that Madrid have failed to win in all competitions, and Los Blancos were fortunate Jon Moncayola did not make matters worse when he struck the post early in the second half.
With Sevilla only able to draw at Mallorca, and Atletico Madrid and Sevilla not in action until Thursday, Madrid – who went closest to scoring when Karim Benzema hit the woodwork – must consider it as an opportunity missed to open up a slight gap on their title rivals.
The little action that did occur happened mostly after the break, with Eduardo Camavinga's effort into the side-netting the highlight of a drab first half.
Madrid out-thought Barca in Monday's (AEDT) Clasico victory, but the slack nature of their performance should have been punished in the 50th minute.
Toni Kroos' tame cross resulted in Osasuna breaking at pace, with Chimy Avila sliding it across for Moncayola, who could only hit the upright.
Madrid was hardly sparked into life by that chance, with the pedestrian pace continuing until Benzema engineered space for a shot that clipped off the crossbar.
Unusually profligate against Barca, Benzema sent another presentable opportunity off target soon after, with Casemiro's effort from in his own half and a wayward Marcelo chip the closest Madrid came to scoring from then on as their recent issues at Santiago Bernabeu continued.