Steve Cotterill had no complaints after Bristol City were dumped out of the Capital One Cup 2-1 by League Two Oxford at Ashton Gate.
The City manager made eight changes from the team which won their opening League One fixture 2-1 at Sheffield United on Saturday and expected a lot more from the replacements, especially after Joe Bryan shot his team into a second minute lead.
But Oxford responded with a positive performance and won the game with second-half goals from young striker Carlton Morris, on loan from Norwich, and substitute Danny Hylton.
Cotterill said: "I'm very disappointed. I certainly wasn't being disrespectful to the competition by making so many changes and I picked a team I was convinced could win the game.
"At Sheffield United I wasn't sure I had selected the right side. Now it seems I did because we only had three players performing to anything like their maximum.
"Oxford were the better side and seemed to want it more than we did. I thought they out-passed us and outran us.
"I gave players the chance to prove that they would have enhanced our performance at Sheffield and not enough of them did. Perhaps some were a bit rusty and they will improve for the game, but all credit to Oxford.
"I didn't want some of my older players to play Saturday, Tuesday, Saturday so early in the season. Maybe we needed a bit more experience out there, but it is a long campaign and we will be okay."
City went in front when a Jay Emmanuel-Thomas shot was blocked into the path of Bryan, who cut inside a defender on the left to curl a right-footed shot into the opposite top corner.
But Morris punished poor marking to volley a 55th-minute equaliser from a corner and Hylton converted a Junior Brown cross with a low finish on 87 minutes to give Oxford a deserved success.
Their manager Michael Appleton said: "The game didn't start as we had planned, but I felt the players responded to conceding the goal with a really good five or six minutes.
"We grew into the game from there and I was delighted by the spirit shown. I love bringing along younger players and we have signed Carlton Morris until January, which gives me time to work with him.
"His goal was reward for all his hard work. Unfortunately, he picked up a bit of a dead leg and I had to bring him off, but hopefully he will be okay for Saturday.
"Sometimes last season when the team fell behind they didn't respond in the right way, but we played ever so well. I thought we did okay against Burton on Saturday, but we never threatened their goal enough.
"We lacked belief in the final third, whereas here we created a number of good opportunities. The result was important and it's great to get off the mark for myself and the players, but the performance pleased me even more."