Fernando Nino added a final goal just over the half-hour mark.
Villarreal rose past Barcelona into third place before Barcelona visits Granada on Saturday.
It was eighth-placed Celta’s third loss of the week, marking a sharp downturn after it won five and drew one under new coach Eduardo Coudet. It lost at Real Madrid last weekend and was embarrassed 5-2 at third-tier Ibiza in the Copa del Rey midweek.
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