It was the third straight loss for Sociedad after opening with a draw when the league resumed. The result left the Basque Country club in seventh place, six points from fourth-place Sevilla in the final Champions League spot.
Sociedad was in fourth place when the league was halted after winning four of its previous five matches. It can drop to eighth after the round is completed. The club was coming off another home loss, against Real Madrid.
“We are not happy with our performance after the break,” Sociedad defender Aritz Elustondo said.
Forward Iago Aspas scored Celta’s winner by converting a penalty just before halftime. It was the team’s second consecutive victory, coming after a 6-0 rout of Alavés.
The Vigo team opened a seven-point gap to Mallorca, the first team inside the relegation zone. Mallorca visits Real Madrid later Wednesday.
Also, midtable Osasuna won 1-0 at Alavés to end its three-match losing streak.