Mark Hughes gave all the credit to Bristol City after seeing his Stoke side dumped out of the Carabao Cup at Ashton Gate.
After the 2-0 defeat at Ashton Gate put the Championship side into the last 16 of the competition, the Stoke boss said: "We were poor and they played very well.
"They will have a good season playing like that, but we have to be much better.
"I am very disappointed because this is a competition we wanted to do well in. Maybe I got the changes wrong, but I was expecting a lot more from my players.
"We changed systems in the first half because we were not coping with Bristol's forward play.
"There were chances for us either side of half-time and when you are not playing well you have to take them.
"We didn't do that either. I know we will be better against Chelsea on Saturday, but that isn't much consolation at the moment."
Hughes continued: " I don't know whether the players underestimated Bristol, but they were certainly warned not to. We just couldn't get our game going and they were better."
Hughes could hardly blame the six changes he made, as Bristol City head coach Lee Johnson made nine.
The Championship side took a 50th-minute lead when Matt Taylor raced onto an Aden Flint header forward. His low shot came back off a post, but Famara Diedhiou was on hand to net the rebound.
The same two players combined again 10 minutes later, Taylor racing onto Diedhiou's flick-on and firing low past Lee Grant with his left foot.
It took some fine Grant saves to prevent a heavier defeat for the Premier League side, who were second best for most of the game.
The home side's assistant manager Dean Holden said: "Every player who comes into the side at the moment is full of confidence and it showed against a top Premier League side.
"We certainly won't get carried away, but the way we are playing we fancy ourselves against anyone.
"I am not saying we can win this competition, but we want to go as far as possible. There is a buzz about the place even in training and the players are working really hard.
"It was great to see Matty Taylor do so well after his injury problems this summer. He doesn't let anything get him down and is very popular in the dressing room.
"Apart from his goal and an assist he kept finding pockets in which to receive the ball and is a clever player in addition to a good finisher.
"I don't mind who we get next. Man United at Old Trafford would be good, but they have to get past Burton first."
Stoke had Grant to thank for not falling behind in the first minute. Taylor put pressure on a Stoke defender and the ball ran to Diedhiou, who was denied by a brave save.
Grant was the busier keeper throughout, but Stoke did threaten just before the break when Aden Flint made two goal-line clearances.
Ramadan Sobhi broke clear in the second half, only to try and lift the ball over goalkeeper Luke Steele and send it tamely wide.