Knights remain third in their group after failing to avenge a 33-20 defeat against Yorkshire Carnegie in the return at Castle Park and had to settle for a losing bonus point when going down 20-18.
With leaders Coventry having lost the previous night at Nottingham, Knights had the chance to regain top spot and looked to be on course to do that when taking a deserved 18-10 lead into the break.
But their second half performance was as miserable as the weather in a game which had little of the traditional derby intensity for long periods despite six men -Â three from each side -Â being sin-binned.
It was a result which left director of rugby Clive Griffiths struggling to come to terms with what he'd just seen.
'It's not often that I'm lost for words but that second half was hard to take and I've got to apologise to our supporters for the performance and the mindless penalties we gave away,' he said.
'We looked energised and in control in the first half and Will Owen scored from a planned move. If we had played like that in the second I would have been satisfied but we let ourselves down. The players don't seem to be listening.'
Knights drew first blood when returning fly-half Kurt Morath kicked them into an early 3-0 lead with a 38 metre penalty.
Morath, who formed a good half-back partnership with the lively Tom James, was wide with a longer attempt at the end of the first quarter.
They increased their lead when Owen ran on to a short ball by hooker Ben Hunter on the edge of the Carnegie 22 and brushed off his immediate marker and then ran strongly towards the line for a converted try.
Carnegie hit back with a converted try by hooker Dylan Donnellan from a long rolling maul which won't have pleased head coach Glen Kenworthy.
The two sides exchanged penalty goals prior to Ollie Stedman, who caught the eye in both attack and defence on his second debut for Knights, touchingÂ down from a catch-and-driveÂ out wide shortly after Carnegie had had a forward sin-binned.
Anyone expecting Knights, briefly down to 12 men in the final quarter, to build on their interval lead in the second half will have been bitterly disappointed as a penalty and converted try without reply saw new leaders Carnegie complete the double.
Knights: Jarvis, Wilson, Creed, Owen, Lewis, Morath, James; Williams, Hunter, Sproston, Challinor, Eames, Tyrell, Hills, Stedman. Rep: Hislop, Mayhew, Quigley, Ryan, Jones, Seniloli, Foley.