Tammy Abraham’s 64th minute tap in from substitute Reece James’ cross ensured that last season’s beaten finalists progressed to the quarterfinal stage, where they will host Sheffield United at Stamford Bridge next month.
Despite dominating proceeding for large spells of the game, Chelsea lacked the cutting edge and Barnsley had two good chances to take the lead before Abraham capitalised.
Tuchel told reporters post-match: "We changed to a back four [at half-time] and took Marcos [Alonso] out for this tactical change. Andreas [Christensen] had to go out because he had a headache.
"The changes made it a little easier to get into the opponents half and overcome the first press.
"We did it well at the start of the second half and played constantly in the opponents’ half.
"We scored the goal and I had the feeling that they increased the risk 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."
Tuchel has now won four of his five games as Chelsea manager and is yet to lose.
