Derby head coach Paul Warne described his side as a “nearly team” after they were beaten 2-1 at home by Oxford.
Mark Harris was the matchwinner for the second time in four days as Oxford deservedly took the points at Pride Park.
The visitors went ahead in the 32nd minute when Curtis Nelson gave the ball away and Cameron Brannagan played in Harris to fire into the top-right corner.
Derby were better after the break but needed a great save from Joe Wildsmith to deny Billy Bodin in the 64th minute although Oxford's clever movement and precise passing was rewarded eight minutes later.
Another slick move ended with Bodin setting up Harris to beat Wildsmith with a low drive.
Derby gave themselves hope when Martyn Waghorn reduced the arrears in the 87th minute but it was not enough to prevent a third home defeat of the season.
Warne said: “We seem to be at the moment, and I include myself because I'm at the front of it, to be a nearly team.
“We nearly score off a set-piece, we nearly score off one across the box, we nearly pick out a man, we're nearly a lot better but at the moment we're not.
“It's disappointing, it wasn't us at our best, I thought we looked nervy first half which surprised me because three-quarters of the team were here last year.
“Oxford are a strong team and I think they'll be up there come the end of the season but whether we showed them a bit too much respect and we keep giving teams a little lift at the moment.
“We were poor tonight and just had too many players off it and we need to get back to it very quickly.”
Oxford head coach Liam Manning said: “I think what you see is a group of players working hard for each other and fighting for the club.
“For me, some of the most impressive stuff tonight was how we defended set-pieces. We stood up to it, we showed bravery, we showed discipline and a real spirit which for me is really important.
“It was an important message at half-time not to try and hold on to 1-0 because when you come to a place like this with the strength they have in their squad if you try and see out a 1-0 for 45 minutes I think you'll be in trouble.
“So I think the lads did a tremendous job of defending when we had to but showing quality in transition and showing quality to keep the ball. I think collectively we were excellent.”
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