Anything but a victory for Barca would probably leave them too much to do with four games remaining, especially as Madrid own the superior record head-to-head.
"It's a massive win," said Ramos. "We knew today was going to be one of the biggest games that we have left. It's always a difficult game away at Bilbao and we saw it like that. We're happy with another crucial three points that put more pressure on Barcelona."
"We're not going to win it thanks to the referees," said Ramos. "People have to look at themselves and be critical of their own performances. Based on the points, it seems we're doing well at the moment."
There were chances at both ends in the first half and Bilbao had the best of them. Williams twice went close but was denied by a block by Marcelo and then a superb tackle by Militao while Raul Garcia's header was pushed out by Thibaut Courtois.
The second half was tighter as both teams slowed in the heat and a more cautious contest seemed to suit Madrid, whose moment came in the 73rd minute.
Bilbao looked tired and never really threatened an equaliser but could have been gifted one had Ramos been penalised for the clumsy collision with Raul Garcia. Ramos survived and Madrid held on.