Michel's side won plaudits for their battling 1-0 home victory over champions Real Madrid last month, and for pushing leaders Barcelona all the way only to lose 3-2 in stoppage time last weekend.
At a noisy Balaidos, however, they conceded a penalty when a freekick hit Hedwiges Maduro on the arm in the wall after an hour, and local favourite Iago Aspas netted from the spot.
As the visitors pushed up in search of an equaliser Enrique De Lucas glanced home a header in the 85th minute to secure Celta's third victory on their return to the top-flight.
Sevilla are fifth with 11 points from seven games, one point and one place ahead of Real Madrid.
Champions Real visit the Nou Camp on Sunday to play arch-rivals Barca, who top the standings with a perfect 18 points from six games.