Debutant Luis Boa Morte failed to inspire new club Chesterfield to victory as Dagenham earned their first away win of the League Two season.
Ex-Arsenal and Fulham winger Boa Morte, who joined the club on Wednesday, played 90 minutes for the Spireites.
But he was upstaged by Sam Williams, who put the Daggers ahead with a low drive before curling in the winner.
Jack Lester had cancelled Williams's opener out, turning in Craig Westcarr's shot for his fifth of the season.
Boa Morte was denied a debut goal - and an equaliser - when visiting keeper Chris Lewington rushed out to block his 67th-minute shot.
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Chesterfield caretaker manager Tommy Wright told BBC Radio Sheffield:
"The first half wasn't good enough, that's for sure. We lacked energy.
"We changed the system and I'll take responsibility for that, it didn't really work.
"I thought it would suit the players, but we changed it at half time and we looked better in the second half.
"We got back in it, a good goal for Jack (Lester) and we created one or two chances and we looked better in the second half."