Dartford suffered a ninth defeat in a row as Paul Clayton scored twice to help Alfreton climb to fourth in the Conference Premier.
Elliot Bradbrook converted an early penalty to put the Darts in front after Darran Kempson had fouled Danny Harris.
But Dartford were reduced to 10 men after Lee Noble was shown a straight red card for a foul on Connor Franklin.
And the hosts fought back to win it as Clayton struck twice in the second half after passes from Dan Bradley.
VIEWS FROM THE DRESSING ROOM
Alfreton Town manager Nicky Law told BBC Radio Derby:
"In the first half, we didn't have any zip about us. We didn't have enough energy and I think too many times the ball was going backwards or sideways and we were getting caught in possession.
"I think we just had to give it a bit of zest when we came out in the second half.
"We were really strong for the first twenty to twenty-five minutes and I think we deserved the win. I really can't complain."
Dartford manager Tony Burman told BBC Radio Kent:
"That game started ok and we felt we could get something from the game. With ten men the guys worked hard, we conceded two goals from a free-kick of ours and a corner of ours on the break.
"We had ten men for the majority of the game, and if you've got chances you've got to put them in.
"There's no luck coming our way, there's none. It's a bitter pill to swallow."
Alfreton Town 15 Worsnop 02 Wood 16 Fenton Booked 05 Wylde 03 Franklin (Wishart - 37' ) 21 Rowe-Turner Booked 10 Bradley 06 Kempson 12 Meadows 08 Shaw (McGrath - 46' ) 09 Clayton Substitutes 22 Akinde 14 Taylor 20 McFadzean 17 McGrath 13 Wishart Dartford 01 Julian 04 Sterling 14 Mitchell-King (Collier - 89' ) 05 Clark 08 Noble Dismissed 10 Bradbrook 17 Martin Booked (Kamara - 81' ) 31 Stevenson 20 Burns 16 Birchall 11 Harris (Cornhill - 81' ) Substitutes 30 Woodyard 06 Cornhill 15 Collier 24 Wellham 36 Kamara
Ref: Darren Handley