Getafe were level in the 18th minute, however, when Pedro Leon picked up a loose ball inside the penalty area before lashing his shot into the bottom corner.
The hosts should have taken the lead just after the half-hour mark. Diego Castro's cross found Lafita inside the box, but the Spaniard could only direct his shot wide from close range when he should have scored.
Sociedad almost restored parity with just over 10 minutes left of the match when Gonzalo Castro sent a low cross into the box, but none of his teammates could get anything on the ball.
It was the hosts who had the best chance late on as Lafita burst into the box, only to somehow drag his shot wide.
The miss wouldn't prove costly, however, as Sociedad failed to find an equaliser in the closing stages.