Ronaldo notched his 72nd Champions League strike to overtake Real stalwart Raul’s previous competition record, recently eclipsed by Barcelona forward Lionel Messi.
The victory was also Real’s 19th straight success in all competitions – a new record for a Spanish club.
Brazilian defender Marcelinho’s red card for handball gifted Ronaldo the opener from the penalty spot, with Gareth Bale, Alvaro Arbeloa and Alvaro Medran also on target.
Real cruised to their sixth straight Group B victory with their routine home success.
Boss Carlo Ancelotti made seven changes to his Real line-up, but crucially retained Kroos, Bale and Ronaldo in a bid for a perfect group-stage return and the Spanish record.
Ludogorets’ outlook blackened with Marcelinho’s dismissal for handball just 20 minutes in. The defender was sent off for blocking Raphael Varane’s header with his hand on the line following a Kroos corner.
Ronaldo strode up and chipped the penalty down the middle, after waiting for goalkeeper Vladislav Stoyanov to commit.
The captain on the night’s expert finish moved him ahead of Real stalwart Raul’s 71-goal Champions League haul.
Kroos then fired in low from long range, only to see Stoyanov tip his effort onto the post as Real clicked into gear.
The hosts doubled their lead before the break when Bale headed home to convert Kroos’ corner.
Fabio Espinho’s curling shot forced Keylor Navas to tip away at full stretch as the visitors forced a rare attacking foray, but Real were in cruise control with a 2-0 lead at the break.
Stoyanov produced five stellar saves in the second half to shut Madrid out time and again, frustrating the otherwise dominant hosts.
The Ludogorets goalkeeper was just about closing in on a clean second half when Madrid finally struck their third.
Arbeloa’s volley proved cruel luck on the visiting stopper, who it initially seemed had completed the save only for the extra official behind the goal to award the goal.
Medran fired the fourth late on when his long-range shot deflected over the luckless Stoyanov.