De Jong has been criticised in recent weeks but scored the winning goal in the 87th minute.
The Dutchman said: "The win was very important because we are in a difficult phase of the season, but we have to improve how we play. It was very difficult here, the pitch was frozen, so it was very difficult to play here."
He continued: "We have to be finer with the ball, especially in the opposition's half. We're going too soon."
De Jong also said he was not happy with the reaction to the Supercopa defeat to Real Madrid, when the team were widely praised despite losing.
"They said we should be proud," he said. "For me, I was embarrassed we were saying we were really proud after the game against Real Madrid. It can't be like that at Barca when you're beaten by Madrid. When you lose, you always have to be disappointed."
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