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Chris Kinnear admitted Dover's performance in Saturday's 2-0 home National League defeat to Barrow was just not good enough.
The Whites boss had hoped his side had turned a corner with the midweek draw at Sutton, but said they failed to build on that display against Barrow.
Substitute Jack Hindle struck twice in the final 20 minutes to give the Bluebirds their first away win of the season – at the seventh attempt.
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Kinnear admitted he had few complaints about the defeat – Dover's fifth already at home this season. Whites remain next to bottom with just one win from their opening 14 matches.
Kinnear said: "After Tuesday we looked like we had turned a corner, we played with a lot of passion but today we didn't really perform as well as we were hoping. It wasn't very good.
"The players were in good spirits but they (Barrow) were a bit better than us. We had a couple of chances at 0-0, throw-ins, corners, but we've let too many goals in.
"From a side that had the second best defensive record (last season), we've gone to not very good defending. We've got to really teach these new ones how to do it."
Kinnear said Barrow deserved credit for the way they played but he felt too many of his players were below par.
He added: "I don't think many people did themselves justice, but we're a team. I've not had a rant and rave with them. I'm sure everybody gave everything they could but today it wasn't good enough.
"I've never had any question about their desire to win. You have bad days, today was a bad day and we've had a few too many to be honest so we've got to get our heads up and get on with it. It's no good whingeing, we've got to try and keep improving somehow."
Whites also suffered a couple of injury blows, the most serious concerning on loan defender George Smith, who has a suspected hairline fracture after a collision with Barrow's Connor Brown.
Kinnear explained: "George Smith is in a bit of a state. He had stitches here and then he's got cuts on his head and he might have some sort of hairline fracture as well. The doctor dealt with it quickly and sent him to the hospital so we'll wait and see what happens."