Stefan Kiessling, the league's top scorer, netted his 13th goal of the season when he headed in a Tranquillo Barnetta cross in the 36th minute. Eren Derdiyok made it 2-0 and Sami Hyypia added a third on 40 minutes with a powerful header.
Felix Bastians pulled one back for the visitors with a solo effort midway through the second half.
Undefeated Leverkusen, who boast the league's best attack and defence, have now won their last four matches, scoring at least three goals in each.
"We had problems in the early stages but once we up our tempo then we also score the goals we want," Leverkusen coach Jupp Heynckes told reporters.
"We have set out to clinch a spot that will lead to Europe football next season and things are looking good for now."
Freiburg were left scrambling in the second half and cut the deficit through Bastians' deft shot at the near post.
"It is far too early to talk about the title," the midfielder, on loan from Bayern Munich, told reporters.
"We continue to chase the targets we have set and we won't change them. We are winning our points and that is working pretty well," he said.
