Bayern Munich, who also crushed Freiburg 5-0 in Heynckes’ first league match on Saturday, completely overran the Celtic defence.
Bayern Munich sacked manager Carlo Ancelotti after his side went down 3-0 to PSG in Champions League on Wednesday.
Champions League wrap-up: The drama peaked at Atletico Madrid’s new stadium where Chelsea trailed at halftime.
Dani Alves, Edinson Cavani and Neymar found the net, with Kylian Mbappe also making his mark with two assists, to put PSG top of Group B with a maximum six points.
Manuel Neuer underwent surgery early on Tuesday which involved setting the fracture with a plate.
Next up for Bayern Munich is a trip to Paris Saint Germain, presumably one team Robert Lewandowski had in mind when he complained that penny-pinching Bavarians needed an injection of world-class talent after falling behind Europe’s elite.
Renato Sanches joined Bayern Munich last season from Benfica for £27.5million after an impressive campaign of Portugal’s Euro 2016 title win. He gained popularity at the competition where he was named best young player.
Newcomers Niklas Suele and Corentin Tolisso put the Bavarians ahead before Robert Lewandowski added a third goal with a penalty, following the official use of the video assistant referee for the first time in the Bundesliga.
Borussia Dortmund banned France forward Ousmane Dembele from playing and training with the side on Thursday after he failed to show for training as Barcelona made a bid reported to be worth 105 million euros ($124 million) including add-ons.
Daniel Sturridge, who was substituted in the second half, scored the final goal of the match with seven minutes remaining for the final whistle but had to be substituted immediately after what looked like a muscle pull in the thigh.
Juventus are aiming to win their fifth successive Serie A title, something they last did in the 1930s.
Mario Goetze came off bench and scored Bayern’s second goal in the 79th minute.
Real were missing the firepower of their regular attacking trio with Ronaldo and Benzema out injured and Bale on the bench.
Bayern struck back with second-half goals from Lewandowski and Mueller but it was a case of too little too late.
Barcelona have the 3-goal advantage going into the second leg at Allianz Arena on Tuesday.