Ronaldo broke the deadlock for Real in the 56th minute with his 22nd Liga goal of the season before Karim Benzema equalled his 11-goal haul from last season to seal the points in the 74th minute.
Real Madrid were five points behind Barcelona and Atletico Madrid just a fortnight ago but with their two rivals having drawn their last two matches, Carlo Ancelotti's men now hold a one-point advantage for at least 24 hours before Barca and Atletico both return to action on Sunday with matches against Malaga and Rayo Vallecano respectively.
Real have also yet to concede a goal in their seven matches across the league and cup since the winter break.
The only sour point on the afternoon was a knock picked up by Gareth Bale early in the match. The Welshman played the remainder of the first half but was taken off at half-time.
In La Liga's other Saturday matches, fifth-placed Villlarreal fell to a surprise 1-0 defeat away at relegation-threatened Valladolid, while Valencia and Espanyol drew 2-2 to remain in ninth and eighth places respectively.
In the late game, Sevilla's hopes of European football were dented as they lost 3-2 at home against Levante, conceding two late goals after being 2-1 up.
The Real Madrid fans produced a spectacular 'tifo' in honour of World Footballer of the Year Ronaldo just before kick-off as he showed off his trophy to his adoring public.
However, his first-half impact was minimal until just before the break when he executed a perfect bicycle kick near the penalty spot from a Luka Modric cross only to see Roberto somehow push it over the bar with an even more impressive save.
Earlier in the half, Roberto misjudged a cross, and Sergio Ramos should have done better than heading over; while Granada's Manuel Iturra also headed on to his own bar; but, in the main, the disciplined visitors frustrated Real admirably.
Real Madrid were better after the break, with Jese on for Bale, and when Ronaldo gave them the lead in the 56th minute, you already felt like the contest was over.
It was a fine goal from the Portuguese forward too – with three men in front of him just inside the area, Ronaldo positioned his feet expertly before drilling a shot through the legs of his marker and into the corner of the net.
He nearly had a second in the 73rd minute when his free-kick hit the back of Pepe and looped onto the crossbar.
However, Ronaldo was involved in the second goal just two minutes later as his fine pass down the left allowed Marcelo to run into the box. The Brazilian flyer looked to have a good angle to shoot but instead he unselfishly rolled the ball across to Benezma who managed to roll the ball into the net despite being somewhat off balance.
After that, Real never needed to get out of second gear for the remainder of the match, as they cruised to their fifth Liga victory in a row.