It was the away side who started the better and Loe might have headed Osasuna into an early lead, but his effort was blocked on the line.
The next real chance of the match fell to Osasuna after 18 minutes, in the shape of Raul Garcia, but his effort from outside the box drifted wide before Loe again missed the target.
The first chance of the second period fell to Betis, via Jonathan Pereira after 52 minutes, but he fired over the crossbar when he might have done better.
Osasuna were reduced to 10 men after 61 minutes when Garcia felled Montero, before the latter came close with an effort after 64 minutes.
Chances remained few and far between in the latter stages, as Betis secured the win.