The Blues eventually left Oakwell with a 1-0 win, Tammy Abraham’s second-half strike setting up an all-Premier League quarter-final against Sheffield United, but only after they had been given a real scare by the Championship outfit.
The hosts went close to opening the scoring twice in the first-half, and Chelsea needed a goalline clearance from Abraham to prevent extra-time late on.
“We scored the goal and I had the feeling that they increased the risk,” Tuchel told the BBC. “But we stepped down in the little decisions. Not enough courage and it was too deep for a long, long time.
“We clearly can play better, so yes I expected more but not in terms that I am frustrated.
“If you lack a rhythm and a bit of self-confidence and you have to show on this pitch, against an opponent that takes all the risk and plays the game of his life, that is not easy. We can do better but I don’t want to be too hard on the players.”
Last season’s runners-up in the competition will host Sheffield United in the last eight, and Tuchel added: “They are organised but I am happy to have a home game. This is what we wanted.”