Cristiano Ronaldo was out again with injury, although he is expected to recover in time for the Champions League final, and captain Sergio Ramos was rested.
Maxi Gomez was threatening for Celta, and the number seven was presented with a half-chance in the 16th minute following sloppy Real Madrid defending, but the centre-forward fired over the crossbar. Isco picked up the ball deep inside his half and played a raking ball for Bale, who cut inside Jonathan Castro and unleashed a left-footed curler into the top-left corner of the goal.
With less than nine minutes to the end of the normal regulation time, Germany worldwide, Toni Kroos competed six goal rout to put Los Blancos three points behind city rivals, Atletico with one game to wrap this season up.
Achraf Hakimi scored his second goal of the season as he got Real's 4th goal in the meeting, while an own goal from Sergi Gomez took the scoreline to 5 - 0 in favour of the Champions League finalists.
Isco added the third goal just moments later with a strike from 20 yards. There was to be no hat-trick for Bale, however, with the Welshman replaced in the 72nd minute of the contest. Koos made it six for the home side with just nine minutes to end the game.
Real Madrid had their fifth in the 74th minute though when Gomez turned a low Asensio cross into the back of his own net.
Zinedine Zidane's side ran out 6-0 winners, and if Bale can contribute in similar fashion to the final league game of the season against Villarreal, the Frenchman might have to deal with a selection headache heading into the Champions League showcase in Kiev.