Los Blancos, who benefited from some questionable refereeing decisions, got the job done in their penultimate league game of the season thanks in large part to another brace from Cristiano Ronaldo.
Celta put up a brave fight in this rearranged fixture, even when reduced to 10 men for the final 30 minutes, but in the end Real proved too strong and now require just one point from their trip to Malaga on Sunday.
Ronaldo fired the visitors ahead through the first attempt of the evening, picking up a loose ball 20 yards from goal and blasting a clean strike past Sergio Alvarez via the legs of Gustavo Cabral - his 19th goal against Celta in 12 games.
Eighteen-goal Iago Aspas grew into the match and had two openings in the space of a minute, first picking out the side-netting when he should have been testing Keylor Navas, before firing a yard wide from the edge of the box.
A big talking point arrived 40 minutes in when the ball popped up and hit Raphael Varane on the arm right on the edge of the penalty area, but the referee failed to spot it and instead booked Aspas for dissent.
Madrid's best spell of the half arrived in the dying embers, as Isco failed to get the ball out of his feet when as good as through, moments before Karim Benzema fared only marginally better when denied by Alvarez between the sticks.
Celta, who knocked Madrid out of the Copa del Rey earlier this season and also beat Barcelona here, had lost all eight games this term that they had trailed at the break.
Any hopes of improving on that record were as good as ended a few minutes into the half after a marginally offside Ronaldo extended his career goals tally against the Sky Blues, latching on to Isco's through-ball and tucking home off the post.
Vigo's task was made all the more difficult on the hour as Aspas was shown a second yellow for a supposed dive inside the area, despite seemingly being shoved in the back by Sergio Ramos.
A bereft-of-confidence Guidetti did give Celta hope of picking up a first point in six outings, benefiting from an Isco error by sending a deflected shot over the reach of Navas.
Just a minute or so later parity was restored, though, as Benzema linked up with Marcelo inside the box and was gifted a tap-in to put Real on the brink of another league win.
Isco was denied by Alvarez from 18 yards out in the remaining minutes and Ronaldo somehow missed from a one-on-one position, but the fifth goal of the night did arrive late on.
Toni Kroos made it look easy, composing himself when spotted by Benzema in the area and picking out the near corner, putting the icing on the cake for champions-elect Madrid with a second 4-1 win in the space of three days.