Unbeaten Leverkusen, now with 26 points, boast a clear lead over Werder Bremen who host Borussia Dortmund on Sunday when third-placed Hamburg SV, also on 22 points, visit Hanover 96.
Leverkusen set a blistering pace in the weekend's first game, scoring in the second minute when Bundesliga top marksman Stefan Kiessling, recalled to the Germany squad, volleyed in from close range after Frankfurt failed to clear in the box.
Despite missing captain Simon Rolfes and striker Patrick Helmes, the hosts dominated the match and before the visitors could recover from the early setback Stefan Reinartz had doubled the lead in the sixth minute with a near-post header.
In-form midfielder Toni Kroos, on loan from Bayern Munich, made it 3-0 with a stinging shot from the edge of the box five minutes later with ex-Leverkusen coach Michael Skibbe quietly looking on as his Frankfurt side were given a drubbing.
Kiessling, battling for a Germany spot ahead of next year's World Cup, could have added to his tally of eight goals this season early in the second half but fired just over the bar.
Leverkusen frustrated Frankfurt, keeping them pinned in their own half, but had to wait until the 86th for substitute Lars Bender to complete the rout with a fine solo effort.
"The team is learning fast," Leverkusen coach Jupp Heynckes told reporters. "(Last week) in Schalke we squandered a comfortable lead (to draw 2-2). Today, after an excellent first half, the team played clever football."
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