This latest victory did not come without a fight in a wind-affected game. Histon had the advantage in the first half when York played poorly, only to see the situation reversed after the interval with the visitors well on top.
Mills's decision to bring on first-choice strikers Michael Rankine and Ashley Chambers after the break and switch from 4-5-1 to 4-4-2 played a major part, Rankine's physical presence being a crucial factor.
Histon had taken a 39th-minute lead through Jim Stevenson's rocket shot from 25 yards and York had to thank Michael Ingham for a great save to deny Lee Wootton a second goal.
But York, who had an effort from Rankine disallowed for offside and a goalbound header by Rankine cleared off the line by Remy Clerima, equalised on 76 minutes, Leon Constantine tapping home after Chris Carruthers's shot had rebounded from the woodwork.
The winner came four minutes from time, Peter Till smashing a tremendous shot into the roof of the net from Rankine's pass.
York, who last tasted defeat in the league on October 30 at Forest Green, have jumped from 19th to 10t in that time.
As for cash-strapped bottom of the table Histon, they appear doomed, facing a five-point deduction at the end of the month and having a playing staff of only six part-timers in addition to amateurs and schoolboys.
York head to Luton tomorrow after the original game was abandoned due to the weather in the second half.
Histon: Welch; Okay, Clerima, Oyebanjo, Mills; L Smith (Okolie 89), Stevenson, Wootton, Attwood (Taaffe 89); Riza, Murray. Unused substitutes: Stewart, Lawton, York.
York City: Ingham; Parslow, C Smith, Young, Carruthers; J Smith, Boucaud, Racchi (Chambers 46); Till, Constantine, Reed (Rankine 56). Unused substitutes: Meredith, Mackin, McDermott.
Referee: S Burt (Northants).
Man of the match: Michael Rankine.
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