The result has Celta closer to LaLiga safety.
Alvarez, who rejected approaches from Barcelona and Real Madrid last year, said: "I am very happy. In the goal, the ball escaped me a little, I hit it as best I could and I was lucky that it went in.
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"It was a game that had been complicated for us with the corner goal that we conceded but the team always showed its face and we knew that in the second half we were going to turn it around.
"We must continue with maximum confidence and ambition because this is not over, there are two games left and we have to go for them and add the remaining six points."