After weeks of looking like the Blaugrana would stroll to yet another title, the gap between the two eternal rivals is now just six points.
Barca are winless in their last two games against Valencia and Athletic Bilbao, with Los Blancos turning the screw on the weekend by beating Atletico Madrid away 3-1.
Ernesto Valverde's side were pretty woeful in the 0-0 draw with Bilbao last night, looking bereft of ideas for much of the game at the San Mames.
Bilbao's in-form striker Inaki Williams should have won the game late on, but the Spaniard brought a miraculous save out of Marc-Andre ter Stegen.
Going forward, Barca's dynamic duo of Lionel Messi and Luis Suarez were far from their best, while Philippe Coutinho continued to look lost in the red and blue jersey.
But it was in midfield where Barca struggled the most.
Valverde opted for a pragmatic trio in the middle of the park of Sergio Busquets, Ivan Rakitic and Arturo Vidal.
And it was Vidal in particular who highlighted to everyone watching the game just how important fellow summer signing Arthur Melo has become already.
The arrival from Gremio is currently sidelined for a month with a hamstring injury and without him, Barca failed to control the tempo and Vidal couldn't get anywhere near replicating his passing range.
You can watch Vidal's sub-standard highlights below.
It's no wonder the Chilean was hauled off just after the hour mark for Carles Alena, with the La Masia product certainly showing his worth when coming on.
Vidal's inclusion next to Busquets and Rakitic - who have been first-choice for years now - really does make little sense for a club like Barcelona.
With the Chilean on the pitch, Barca have no one to operate in the 'Andres Iniesta role' and it means Rakitic has to play further forward - something he isn't particularly great at doing anymore.
Valverde needs to find a midfield answer in Arthur's absence and Alena seems the most viable option right now.