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Dover manager Chris Kinnear bemoaned the goals which ended Whites' four match winning run in National League.
Keeper Steve Arnold slipped over on his line as Jordan Maguire-Drew's overhit cross from deep sailed straight into the net to break the deadlock early-on and the home defence were missing in action when evergreen Paul Benson headed home a corner just before half-time.
The hosts did improve after the break and Ricky Miller won and missed a penalty before hooking home a volley to ensure a tense final 15 minutes, however the classy Daggers saw the game out to leapfrog Dover and return to the play-off places.
Kinnear admitted: "It was a couple of bad goals. That first one, there was nobody else in the penalty box. He was just going to catch it, they had given up on it and he's just slipped over. He's actually sat on his backside and it's curled into the goal. It's a freak goal.
"It was a bit of a shock, I've got to say. It's not one I've seen happen very often."
He added: "Then they scored right on half-time, we didn't mark very well from another dead ball. That's the way they play, their looking for deadballs, Dagenham.
"Second half we did a lot better, we had a go, we missed a penalty, scored (but it's) one of those things. You can't win every game."
It was a sixth game in 16 days for Dover and Kinnear claimed: "The lads have been magnificent the last six or seven games. You're going to have a bad half every now and again, that first half was just one of those days.
"(The opening goal) did knock the stuffing out of us, it shouldn't do, we're not going to blame people or point fingers, they've all done well for us.
"You're going to get beat sometimes. We don't get too down just like we didn't get too carried away with the 6-0 win the other day.
"If we'd scored the penalty things could have been different. We'll move on, we won't get down, we've got a lot to play for this year.
"It was one of those days where we didn't really play as well as we have been doing. You're going to lose games sometimes. we've got to regroup, have a good think about it and move on."
After their 23rd game of 46 this season, Dover sit sixth with 43 points and Kinnear claimed: "It's been a brilliant start," before adding: "Another seven points and we won't get relegated."