Witsel, Reus score late as Dortmund win in German Cup
Dortmund was on the verge of a first-round exit at the hands of the second-division club before Belgium midfielder Witsel - who had come on with just 15 minutes remaining - scored in the fifth minute of injury time to send the game to extra time. Reus then followed up with his own injury-time winner.
Dortmund, the 2017 champion, had failed to impress in Lucien Favre's first competitive game in charge, and it paid the price when Sebastian Ernst scored late for Fuerth.
Witsel, who joined Dortmund from Chinese side Tianjin Quanjian, was set up by Reus, who was the beneficiary of Jadon Sancho's incisive play for the winner - after goalkeeper Roman Buerki denied Fuerth's Fabian Reese in a one-on-one.
Fuerth coach Damir Buric missed the game due to a family bereavement.
Earlier, Freiburg needed penalties to get past third-division Energie Cottbus. Tim Kruse missed the decisive spot kick as the Bundesliga side won 5-3.
Hertha Berlin won 2-1 at Eintracht Braunschweig and Paderborn enjoyed a 2-1 win over Ingolstadt.
Defending champion Eintracht Frankfurt was knocked out at the first hurdle by Ulm on Saturday, when Bayern Munich struggled to overcome fourth-tier SV Drochtersen/Assel 1-0.