Huddersfield's win kept them in the hunt for automatic promotion from League One and put Dagenham & Redbridge into the relegation places.
Jordan Rhodes slotted Town into the lead, before Romain Vincelot offered the Daggers hope of avoiding the drop when he found the top corner for 1-1.
But Rhodes headed his second from six yards to grab the win and extend the hosts' unbeaten league run to 23 games.
John Akinde wasted two great chances to secure a vital point for the visitors.
Dagenham & Redbridge slipped from the safety of 20th position to 21st spot, and are now one point adrift of Walsall.
At the top, Huddersfield kept up the pressure on second-placed Southampton and stay level with their rivals on 83 points, although the Saints have a game in hand and a vastly superior goal difference.
Huddersfield Town manager Lee Clark told BBC Radio Leeds:
"We've won a game today when we haven't been at our best, which tells you about the group of players we've got.
"I said to them after the game, and not being disrespectful to the group I had last year, but last year we would have ended up with one point, possibly might have even lost it because of the pressure we would have been under.
"It wasn't one of our better performances but we march on and I think the fans would rather take that today than us being on scintillating form and either drawing or losing the game."
Dagenham and Redbridge boss John Still told BBC London 94.9:
"They're a top side but second half it was all us and on the replay it looked a penalty on John Akinde.
"They were always going to cause us problems today but some of our play and movement showed that we can play and take that performance into the next two games.
"When we play it, we're hard to contain and the games left are tough games and this is an unbelievably tough league."