Alex Meier put the visitors ahead with an early goal, before Henrikh Mkhitaryan levelled with a 24th-minute tap-in.
Pierre-Emerick Aubameyang, Mats Hummels and Adrian Ramos all netted in a scintillating second half for Dortmund, who missed a dozen more clear scoring chances as they rode roughshod over a frustrated Frankfurt.
Bundesliga top scorer Aubameyang took his goal tally to 18 despite shooting wide with a 44th-minute penalty after Slobodan Medojevic was sent off for a second booking.
Dortmund, who bounced back from their midweek Europa League defeat at PAOK Salonika, are on 38 points with a nine-point advantage over third-placed Hertha Berlin. Eintracht dropped to 15th on 14 points after their fourth straight loss, adding pressure on embattled coach Armin Veh.
Dortmund maintained their unbeaten run at home in the league, having won seven of eight matches at their Signal Iduna Park stadium this season.
Bayern are top with 43 points after beating Ingolstadt 2-0 on Saturday, with one more matchday left until the winter break.
Augsburg's Brazilian forward Caiuby fired home a stoppage-time volley to give them a 2-1 victory over Schalke 04 that lifted them out of the relegation zone and piled more misery on their free-falling opponents.
Hong Jeong-ho gave Augsburg the lead when he backheeled a Dominic Kohr shot into the net in the 34th minute, before Schalke levelled in the 70th with a well-worked goal from Sead Kolasinac, his first in the Bundesliga.
Caiuby, however, scored in stoppage time with a left-footed volley following a poor clearance from Benedikt Hoewedes to secure a second consecutive Bundesliga victory for Augsburg, who were buoyed by reaching the last 32 of the Europa League in midweek.
Augsburg moved up to 13th in the table on 16 points while Schalke, who have won just one in their last seven, dropped to eighth on 24.
(Reporting by Karolos Grohmann; editing by Toby Davis)
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