Villarreal missed the chance to climb into the top three as they were beaten 1-0 by Real Betis in the day's late game.
The crucial goal came in the 37th minute when Joan Verdu's shot was saved by Sergio Asenjo and Nosa Igiebor slotted in the rebound.
Osasuna remain in trouble at the foot of the table after an ill-disciplined performance cost them in a 1-0 defeat at home to Levante.
Jordi Xumetra grabbed the decisive goal in the 87th minute when he was quickest to react after Papakouli Diop's penalty was saved by Andres Fernandez.
Osasuna's day got worse when substitute Alvaro Cejudo was sent off in the final minute for a second bookable offence.
Elche picked up their first victory of the season, and a first in the Primera Division in almost a quarter of a century after beating Celta Vigo 1-0.
The promoted side, back in the top tier for the first time since the 1988-89 season, snatched all three points thanks to a precise Javi Marquez finish on 62 minutes.
Getafe claimed a surprise 2-0 success away to Espanyol courtesy of an Adrian Colunga double in the second half.
The hosts were looking to bounce back from their first defeat of the Primera Division season at Villarreal in midweek, but were undone by Colunga's brace.
Substitute Pablo Sarabia set up both goals as Colunga netted in the 73rd minute and again in stoppage time.