City's win in the first north-west derby of the 2019 league campaign.
Deasy sent off for horrendous tackle on City's Coll and Harps with a disallowed goal as sides went in 0-0 at half-time.
In the second half Aidy Delap put City in front before Nathan Boyle's equaliser. A double from David Parkhouse had Derry back in the driving seat and a penalty with the last kick of the game wasn't enough for Harps.