Bale was joined on the scoresheet by Isco, Achraf Hakimi, Toni Kroos and Celta defender Sergio Gomez as the Madrid giants returned to within three points of second-placed Atletico Madrid with just one round of La Liga matches left to play this term.
Hakimi had the home side's first half-chance of the match in the sixth minute after breaking into the Celta box, but the right-back just could not squeeze the ball under Sergio Alvarez.
Madrid did make the breakthrough in the 13th minute, however, when Bale raced onto a through-pass from Modric before finding the back of the net via the inside of the post.
Maxi Gomez was threatening for Celta, and the number seven was presented with a half-chance in the 16th minute following sloppy Madrid defending, but the centre-forward fired over the crossbar.
Jozabed then had the ball in the back of the net for the away side only to see the offside flag spare Real's blushes, with the hosts becoming increasingly untidy at the back.
Zidane's team continued to knock on the door down the other end though, and doubled their advantage in the 30th minute when Bale cut inside before finding the top corner with a wonderful finish.
Isco then made it 3-0 to the European champions just two minutes later when he curled the ball beyond Alvarez from outside the box.
Hakimi continued to cause Celta problems down the right in the early stages of the second period, and the 19-year-old was rewarded in the 52nd minute when he found the back of the net through the legs of Alvarez.
Isco then flicked a Benzema effort into the Celta goal in the 58th minute, but the offside flag cut the home side's celebrations short, before Alvarez just beat Bale to a through-ball from Kroos.
Marco Asensio and Borja Mayoral came off the home side's bench just past the hour, but the pattern of the match did not change as Los Blancos continued to look for more goals. There was to be no hat-trick for Bale, however, with the Welshman replaced in the 72nd minute of the contest.
Real Madrid had their fifth in the 74th minute though when Gomez turned a low Asensio cross into the back of his own net.
Mayoral then brought a smart save from Alvarez in the 78th minute as the home side continued to force the issue, and they had their sixth in the 81st minute when Kroos found the far corner following good work from Mayoral.
Modric hit a post for the home side six minutes from time, and despite a host of late pressure, Celta managed to escape without any further damage in the final moments.
Real will finish their La Liga campaign away to Villarreal next weekend, while Celta, who remain down in 13th position in the table, will end at home to Levante.
REAL MADRID (4-3-3): Navas; Achraf, Nacho, Varane, Marcelo; Kroos, Casemiro, Modric; Bale (Lucas 72'), Benzema (Mayoral 64'), Isco (Asensio 64')
CELTA VIGO (4-3-3): Sergio; Mallo, Roncaglia, Gomez, Jonny; Lobotka, Wass, Jozabed (Radoja 71'); Mendez (Aspas 82'), Gomez, Boye (Hernandez 46')