With heavy rain making passing football near-impossible, Barcelona found a way with Alexis Sanchez's botched header, Lionel Messi's brace and Cesc Fabregas' late goal washing out Alberto Moreno's opener.
Despite the comfort of the scoreline, Barca had to survive their post being hit when a goal down and also had to rely on Victor Valdes to make a number of impressive saves.
"We're aware that we're at a crucial part of the season, the match could have been tied up 2-2 but we managed to control the end of the match," said Barca coach Tata Martino.
"Being first brings tranquility, now the game starts to see who doesn't fail."
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