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Jay Saunders told Maidstone players they had cheated themselves with their first-half performance against Maidenhead.
United trailed 2-0 at the break after Callum Driver conceded a penalty midway through the half, followed by a soft goal in injury-time.
Frannie Collin scored a late spot-kick after United dominated the second half but Saunders' side suffered their first defeat in 11 National League South games on Tuesday night.
The Stones boss said: "I just said to them in there I kind of feel they've cheated themselves by playing that way for the first 45 because we looked tired, we didn't move the ball, we weren't picking up seconds.
"You can't just come out second half and switch it and all of a sudden be on the front foot and be positive.
"They let themselves down really with that first 45 but I can't be too harsh.
"It's August since we lost and we've just got to get back on another run as quick as we can."
Saunders was frustrated with the goals Maidstone conceded, having been so strong defensively all season.
He added: "I don't think there's any need for Callum to make the challenge he has to give the penalty away and then the second one the fella's been allowed to pick up the ball on the halfway line and wander through.
"Second half we threw everything at them and we were quite dominant but by that time, at two goals up, they're going to sit back and defend and we couldn't get the breakthrough."