German Cup: Dortmund edge past Hoffenheim, Freiburg dumped out
In an entertaining first half, Hoffenheim had enough chances to take the lead, but it was the hosts who broke the deadlock in the 43rd minute when Jamie Bynoe-Gittens found enough space down the left to feed Reus inside the box and the midfielder rifled a curling shot into the top corner.
Hoffenheim ended the game with 10 men after Ozan Kabak was sent off with a second booking in second-half stoppage time.
Dortmund have now won each of their three German Cup encounters against Hoffenheim.
Bundesliga leaders Bayer Leverkusen also advanced with a 5-2 win at Sandhausen.
Bundesliga club Freiburg crashed out of the competition after losing 3-1 at home to second-tier Paderborn.
Bayern Munich are in action later at third-tier Saarbrucken.