Casemiro was Real Madrid's unlikely hero as he hit the winner to open up a five-point lead on Barcelona at the top of La Liga with a 2-1 win at Athletic Bilbao on Saturday.
Karim Benzema fired the visitors into a half-time lead from Cristiano Ronaldo's cross.
Aritz Aduriz briefly levelled for Athletic, but Ronaldo again was involved for the winner on 68 minutes as his flick-on was slotted home by the unmarked Casemiro for just his third goal of the season.
Barcelona can cut the gap back to two points when they face Valencia at the Camp Nou on Sunday.
Athletic were undefeated in 19 games at home in all competitions stretching back to August and started confidently with Inigo Lekue threatening early down the left.
His dangerous cross was bundled just wide by Inaki Williams inside the first two minutes.
However, Madrid settled after the first 10 minutes and had the ball in the net in their first serious attack only to be denied by the offside flag.
Dani Carvajal timed his run to meet Benzema's through ball but he squared to Ronaldo when going for goal would have been the better option, and the World Player of the Year's tap-in was ruled out.
Six minutes later Ronaldo was denied again, this time by a stunning save from Kepa Arrizabalaga as the young goalkeeper leapt low to his left to turn the ball to safety.