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."
Chesterfield 13 O'Donnell 04 Forbes 05 Trotman (Darwikwa - 62' ) 06 Hird 16 Ridehalgh 08 Togwell (Randall - 73' ) 17 Atkinson 25 Talbot 11 Westcarr (Boden - 81' ) 14 Lester 37 Boa Morte Substitutes 27 Wilson 12 Darwikwa 15 Clay 23 Randall 18 Boden 19 Hazell 29 Evans Dag & Red 01 Lewington 02 Wilkinson Booked 03 Ilesanmi 04 Doe 06 Spillane 12 Elito 15 Saunders 17 Howell 19 Ogogo 07 Williams 20 Gayle Substitutes 30 Seabright 18 Hoyte 28 Santos 11 Do Green 16 Maher 14 Reed 23 Woodall