The coach was thrilled as his side beat Saarbrucken 2-0 and set a club record for possession percentage in a competitive match in the process
Goals from Julian Schieber and Jonas Hofmann sent the Schwarzgelben into the last 16, while the team achieved 84 per cent possession - their highest total ever tallied in a competitive match.
Klopp doubted the third division side would pose a huge threat but was thrilled to see second-string players shine in the cup clash, with only his team's finishing letting him down.
"An upset was never on the cards," the coach, 46, told the club's official website. "We played a great game even if it only finished 2-0.
"Our finishing could have been a bit better but everything else was perfect. It was fun to watch.
"The lads with little match experience played a fantastic game: Jonas Hofmann, Julian Schieber, and Oli Kirch was the outstanding player. They were really good! It looked fluid despite little playing time."
Dortmund, who sit third in the Bundesliga, can go second behind leaders Bayern Munich if they win Saturday's clash at home to Bayer Leverkusen.