It could have been a different outcome, however, had fly-half Simon Humberstone, who only hit the target once, had his kicking boots on.
The one consolation for Knights, who defended better than in their six-try defeat at home to Cornish Pirates, was the fact they picked up two bonus points.
But with Bedford, who visit Castle Park next weekend, beating third-placed Nottingham, they dropped to fifth.
The home side, who had won three on the trot prior to going down at Nottingham last time out, opened the scoring with a penalty by full-back Rob Kilby after Knights had been caught offside at a first-minute ruck.
Humberstone, again preferred to Declan Cusack at fly-half, failed with a chance to level the scores two minutes later
A scrum penalty saw Humberstone take play into the Richmond 22 for the first time where centre pairing Will Owen and Lloyd Hayes both make their presence felt. Knights also went close from a catch-and-drive.
Richmond not only weathered their first pressure of the game but extended their lead at the end of the first quarter.
Knights lost the ball in contact and that gave the home side the chance to counter and finally score a try through wing Martin Freeman after the ball had been moved along the line from a short lineout.
Kirby added the extras and also kicked a second penalty to leave Knights, who had posted their biggest away win of the season on the same ground last year, trailing 13-0.
Knights knew that they had to score the next try to avoid the risk of losing touch with their mid-table hosts.
Another Humberstone penalty into the corner, following good work by No 8 Aaron Carpenter in the build-up, gave Knights another go at a catch-and-drive from which veteran prop Colin Quigley, who only scored his first try for the club this season, forced himself over from close range just short of the half-hour mark to make it 13-5.
Buoyed by the score, Knights were in again on 32 minutes. Full-back Charlie Foley, another of the injured players to return, broke the line from a lineout just inside the Richmond half and raced into the home 22 before finding the speedy Tyson Lewis with a long try-scoring pass.
Humberstone’s conversion, which would have levelled the scores, came back off the woodwork.
Kilby gave his side a bit more breathing space when kicking a third penalty to make it 16-10.
Knights continued to make life hard for themselves and only good defence denied Richmond, who subsequently converted a fourth penalty to lead 19-10, from a botched lineout in their 22.
Knights were quick out of the blocks after the restart and, after Lewis had gone close, drove over in the corner.
Humberstone again failed to add the extras leaving Knights, who had scored three tries to one at that stage, trailing 19-15.
Knights finally got the noses in front on 51 minutes. Hayes produced some classic centre play after the ball had been moved from a lineout to send Tom James over just three minutes after he had replaced scrum-half Michael Heaney.
As well as the bonus point try Doncaster supporters also cheered Humberstone’s first successful kick of the night.
But if they thought that Knights would pull clear in the final quarter they were to be mistaken and only the sort of committed defence missing against Pirates, denied flanker Jack Allcock a 70th minute try.
The home side were not to be denied, however, and a spell of intense pressure resulted in a late match-winning converted try.
Knights: Foley, Bulumakau, Hayes, Owen, Lewis, Humberstone, Heaney; Evans, Hunter, Quigley, Challinor, Civetta, Ram, Hills, Carpenter. Rep: Bergmanas, List, Sproston, Hicks,Shaw,James, Cusack.