Having seen Real Madrid go top on Saturday, the Catalan side joined their bitter rivals and also Atletico Madrid thanks to a come-from-behind victory on a torrid night.
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.
Humberto Osorio scored twice in the second half as Valladolid fought back from two goals down to salvage a 2-2 draw at home to fellow strugglers Elche.
Ferran 'Coro' Corominas had given Fran Escriba's side the lead in a scrappy first half that was low on attractive football, and Manu del Moral looked to have sealed the points when he doubled their advantage on 66 minute.
However, Colombian forward Osorio scored twice in seven minutes to earn Valladolid a valuable point that not only puts them three points from safety, but also prevents Elche from moving seven points away from them.
Osasuna moved further away from the relegation zone as they claimed a 2-0 over Getafe.
Oriol Riera fired them ahead early on but it was backs-to-the-wall stuff for most of the first half as struggling Getafe dominated proceedings.
Osasuna improved in the second half and eventually got a second goal through Roberto Torres as the home side moved five points clear of the drop and extended Getafe's winless league run to eight games.
Real Sociedad passed up an opportunity to put pressure on Athletic Bilbao in the hunt for fourth spot as they were held to a goalless draw at home to Levante.