It was always on the cards that, after the supreme effort to win at Wharfedale the previous Saturday, Park would not be able to repeat such a stunning performance the following week.
And so it was, Park went down 12-15 at home to struggling Blackheath, meaning they are now seven points behind National League One leaders Doncaster Knights.
Blackheath continue to flirt with the relegation places, lying fourth from bottom.
All credit must go to Blackheath who were good enough to take advantage of an error-strewn home performance and certainly deserved their victory.
The very muddy pitch and squally wind helped neither side, but after an even opening period, Park began to get the better of proceedings through their dominant scrum.
They had to overcome lock Richard Boyle incurring an early sin bin for a professional foul, but after some promising forays, earned a scrum 10m from the Blackheath line.
Like a bar of soap: The ball squirts free in the tackle
After meeting stern resistance it was winger Charles Broughton who crossed close to the corner to put Park ahead by 5-0.
Generally, Park held the whip hand at this stage, but where passes had stuck the previous week, this time any number of promising moves were marred by handling errors, many induced by some committed defending on the part of the visitors.
A score seemed likely when Park drove a Blackheath scrum backwards to win a penalty, which was belted to the corner, but they failed to press home their advantage.
Soon after, flanker Harry Broadbent looked to be through with a scoring chance but the ball was spilled in an attempted tackle.
Blackheath had a rare chance to get onto the scoreboard on 18 minutes when fly half Simon Whatling attempted a long range penalty.
He got the line correct, but it passed under the crossbar.
As the game progressed, Blackheath began to look a lot more comfortable.
They forced Park to display their own defensive skills and – just as the danger looked to have passed – winger Hamish Graham got round the defence to score in the corner for 5-5 on 33 minutes.
Whatling could not make a near-impossible conversion, but it was points Park will be disappointed to have conceded.
For the remainder of the period it was Blackheath who were mostly in the driving seat.
Just before half-time they had a penalty chance which Whatling was unable to convert.
Hand off: Charlie Broughton holds off a Blackheath challenge
At the end of added time a Park raid yielded a penalty, but with the referee waiting to signal the interval there was no time to kick for position.
Sneddon had an unsuccessful pot at the posts from a nigh on impossible position given the wind.
The second half started with one of those bouts of aerial ping pong, in which Park finished a distant second, but they played their way out of trouble and began to look good again.
A penalty to the corner saw them fail to take advantage, but they built up pressure and on 10 minutes their powerful scrum forced Blackheath backwards to eventually claim the penalty try, converted by Sneddon for 12-5.
It looked as if Park might now kick on for the two tries they needed for the bonus point win, but Blackheath had other ideas and wrested back the initiative.
Two scores in five minutes rocked the hosts. First Whatling reduced the margin to 12-8 with a penalty on 52 minutes, then a strong scrum five minutes later saw flanker Dave Allen touch down, converted by Whatling for 15-12.
Park were now facing an uphill battle against a rampant Blackheath side who scented blood. The harder Park tried the more difficult it got.
A series of technical offences, in addition to the handling errors, saw them concede possession far too often to build cohesive attacks.
What you looking at? Pete Hodgkinson spies a gap in the Blackheath lines
Blackheath, tails up and now enjoying a clear advantage in possession, were never going to make it easy for them as the clock became their 16th man.
With five minutes left, Park saw a glimmer of light as their scrum drove out of defence and visiting prop Cai Griffiths received a yellow card for stopping it by illegal means.
But reduced to 14 men, Blackheath were in no mood to surrender their hard won lead.
The game entered its last play with Park in possession in their own midfield.
They did well to carefully work the ball to close to the visiting 22 but when the seemingly inevitable handling error occurred Blackheath claimed a deserved win.
It was never going to be a great match in the conditions, but it was a compelling local derby. Park will doubtless be determined to show Worthing, whom they visit next week, that this was no more than a bad day at the office.
Park: Lewis-Pratt (Gower); Broughton, Hodgkinson, Staff, Edgerley; Sneddon; Grant (Dash); Liffchak, Bellamy, McKenzie; Ball, Broadbent (Starling), Ellis.
Subs (not playing): Cobb, Ovens.
Up on high: Rosslyn Park's Richard Boyle rules the line-out
Here: Pete Hodgkinson offloads