He fumbled a cross on 83 minutes as Kris Doolan tapped home the winner.
Boss Terry Butcher said: “It was just one of those games where it wasn’t going to happen for us and then we get a sucker punch at the other end.
“Dean Brill, who has been absolutely magnificent for us all season, makes his first mistake at the club and it has cost us three points.
“But it wasn’t just Dean’s mistake, we were very haphazard in the final third.
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“I’m really disappointed to lose a game which we should have got at least a point from.”
Defender Lathaniel Rowe-Turner returned for Alfreton Town and played the full game as they triumphed 3-2 at Aldershot Town in the Skrill Premier, while striker Scott Rendell played the full 90 minutes as Woking went down 2-0 at Wrexham.
Full-back Jerome Jobodu was an unused sub as Boreham Wood lost 1-0 at Basingstoke Town in Skrill South, while young striker Jake Woolley netted his third goal of the week as he sidestepped a defender close to the byline and fired home a narrow 39th-minute effort as St Neots Town won 3-1 at Halesowen Town in FA Trophy first round qualifying.