The frontman finally killed off a tenacious Kidderminster side by bagging a coolly taken winner.
After a scrappy first half neither side looked like breaking the deadlock until Farrell's moment of magic wrapped up the points.
Kidderminster looked the more threatening side in the opening half an hour and Lee Thompson came close to handing the visitors the lead, but his fierce header was blocked thanks to an acrobatic clearance from Chris Todd.
Simon Russell then carved out another gilt-edged opportunity after crossing for Michael Blackwood, who planted a stinging header straight at Paul Jones.
The visitors continued to pile on the pressure and Thompson was once again denied as his piledriver whistled past the post.
But City almost snatched the lead on the stroke of half-time but Andy Taylor's volley was touched around the post by John Danby.
It was Kidderminster who set the early pace at the start of the second half and Iyseden Christie lofted a shot narrowly over the crossbar and then Gareth Sheldon almost came back to haunt his former club when he seemingly handed Kidderminster the lead.
But his close-range effort was ruled out for offside, much to the bemusement of the winger.
The game exploded into life halfway through the second period when Lee Phillips put Farrell in the clear and the former Carlisle United striker made no mistake with a deft finish.
From then on it was the home side who continually pressed forward in a bid to seal victory.
Skipper Glenn Cronin came close to wrapping up the win, but his shot crashed against the foot of the post and away to safety.
Lee Phillips was also denied when Mark Jackson made a last-gasp clearance to block his goalbound effort.