Kolo Muani double helps Frankfurt beat Darmstadt 4-2 in German Cup
The hosts, who face Napoli in the Champions League Round of 16 on February 21, went through after Kolo Muani scored a double having also struck twice in the league on Saturday.
The France international, who has enjoyed a meteoric rise in the last few months and also played in the World Cup final in December, struck with their first chance of the game, looping a header over Darmstadt keeper Marcel Schuhen in the sixth minute.
It should have been 2-0 in the 23rd but Mario Gotze could not beat Schuhen from close range.
Instead it was Darmstadt who scored through Mathias Honsak, also a double scorer last week in the second division, completing a quick break after Frankfurt defenders were caught completely out of position.
Honsak bagged his second goal just two minutes later before Rafael Borre drew the hosts level a minute before half time.
Eintracht, German Cup winners in 2018, turned the game around in the 63rd with a textbook passing move with Kolo Muani heading the ball back for Daichi Kamada to thunder it in from just outside the box.
Kolo Muani then capped his fine performance with another goal in the 90th minute after Goetze had sent him through with a pinpoint pass.