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.
Leverkusen restored their two-point lead over Bayern, who had briefly gone top on Saturday after their 3-0 win over Mainz.
Schalke 04 remained in third place, a further point behind, following their 2-0 victory over Hoffenheim.
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.
Yet for the first half hour it was the visitors who were more aggressive and were only denied an early lead by two spectacular saves from Leverkusen keeper Rene Adler.
"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."
INNOCUOUS CROSS
The hosts only needed half a chance to score and they got it when Swiss international Barnetta lifted a seemingly innocuous cross into the box in the 36th minute.
Kiessling beat his marker to head in and end his 486-minute goal drought.
The hosts were gifted a second goal 66 seconds later with Freiburg keeper Simon Pouplin fumbling a pass forward, sending the ball to Derdiyok who had no trouble beating the hapless Frenchman for his eighth goal of the season.
Just three minutes later veteran defender Hyypia exploded into action to score with a powerful header from a Toni Kroos corner.
Freiburg were left scrambling in the second half and cut the deficit through Bastians' deft shot at the near post.
Leverkusen playmaker Toni Kroos, who has been outstanding this season, played down title talk.
"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.
