Last season's Bundesliga top-scorer Stefan Kiessling put them in front before Mike Hanke opened his account for Freiburg just before the break.
But Heung Min Son and Sidney Sam both struck early in the second half to kill off Freiburg, who played up the chance to get back into the game when Jonathan Schmid had a penalty saved.
Kiessling netted 25 times last season and he needed just 22 minutes to open his account for 2013/14.
Stefan Reinartz lifted the ball up inside the penalty area and one of the tallest players on the field rose to meet it, beating Matthias Ginter in the air and looping the ball over Oliver Baumann to give Leverkusen a deserved lead.
Hanke led Freiburg's riposte and after going close twice, he brought Christian Streich's men level five minutes before half time.
Schmid was the provider, teeing up the former Borussia Monchengladbach striker to score from 10 yards out.
It was rather harsh on Leverkusen, who had dominated the first half, but they soon regained their lead with Son keeping up with Sam as he broke through, and accepting his team-mate's gift from close range.
Five minutes later, Kiessling set up Sam to make it three with a composed finish.
The deadly attacking trio looked a threat each time Leverkusen went forward with Sam's pace causing a whole host of problems to a Freiburg rearguard which looked like it could collapse at any moment.
Instead, Freiburg drew courage and earned a penalty when Oliver Sorg went down under the challenge of Lars Bender.
Schmid took responsibility for the penalty, but he was denied by Bernd Leno.
With that save, Freiburg's hopes of a recovery evaporated and Leverkusen played down the clock.