Their Copa del Rey victory was the first time they had won the cup since 1998 and was their first piece of silverware in two seasons.
Barcelona currently have 86 points and a goal difference of plus 72 with three games left, while Madrid have 78 points with two to play.
Their triumph came on the same day that their Champions League rivals United claimed their third successive English Premier League title with a 0-0 draw against Arsenal.
The pair meet in Rome with United looking to defend their European title.
Barcelona's success this year has vindicated their decision to part company with long-standing coach Frank Rijkaard at the end of last season and appoint former player Guardiola as manager.
For 38-year-old Guardiola, a Catalonian by birth, this week's triumphs are his first as manager of the club he spent 11 years playing for.
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