Santiago Solari gave Isco a minimal role in his plans but, after Zidane was reappointed to end the Argentinian's ill-fated tenure, the Spain international returned to the starting XI alongside the similarly ostracised Bale, Marcelo and Keylor Navas.
Bale hit the crossbar and was fortunate not to be sent off, while Navas brilliantly prevented Maxi Gomez from putting relegation-threatened Celta ahead amid an all-action showing from Marcelo.
But it fell to Isco to break the deadlock after the hour and Bale made sure 13 minutes from time, moving Madrid two points behind city rival Atletico Madrid in second ahead of its trip to Athletic Bilbao.
Navas, preferred to Thibaut Courtois in goal, made a stunning reaction save from Gomez's 16th-minute header and Celta retained a threat on the counter-attack throughout.
Bale struck a 30th-minute scissor-kick against the bar and Sergio Ramos headed wide after Ruben Blanco diverted a rasping Marcelo strike behind.
The Wales forward crossed for Karim Benzema to roll into the net during first-half stoppage-time but was correctly penalised for crashing an elbow into Kevin Vazquez's face and fortunate to only see a yellow card.
Unperturbed, Bale went sliding into Sofiane Boufal in the 53rd minute, the act of turning his studs to the ground before contact enough to spare him.
Modric thought he had given Madrid the lead when he drove home from Toni Kroos' partially cleared corner, only for a Raphael Varane to be ruled offside and interfering by a VAR (video assistant referee) review.
The breakthrough came after the hour as Madrid constructed the type of sharp break that became a hallmark of Zidane's initial reign and Isco slid home Benzema's low cross before departing to a standing ovation.
Blanco excelled to thwart Bale and Benzema, but the former skipped through a flagging backline to clip in a right-footed shot off the post.