Harriers continued to pour forward after their goal with Ducros in particular getting into plenty of shooting positions.
The striker took aim from 20 yards on 68 minutes and Collett fumbled his drive but the oncoming Smith could not guide the ball into the net.
Then the former Coventry striker then tried an audacious effort from the edge of the box but it was well off target.
Ducros followed it with a low shot from an angle which was blocked by Collett after persistent efforts from Foster on the left.
Darlington brought on midfielder Campbell, who scored the winner in this season's FA Cup tie, for Maddison on 78 minutes before Harriers replaced Foster with Broughton 10 minutes from time.
Henriksen placed a shot just wide on 83 minutes when Ducros laid a good ball into his path.
But Darlington's cause was made all the more difficult two minutes from time when Betts was sent off for his second bookable offence after flooring Broughton with a tackle on the left flank.
Darlington were awarded a controversial free-kick in injury time but keeper Brock went down to collect a tame effort from defender Brightwell.
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