Ed Volley’s early try was converted by Ed Morgan to put the visitors in front, only for Tighe Maxwell-Whiteley and Jack Jolly to level for Mose.
Park’s duo restored the advantage, but it was 14-14 after Jolly added to a Ben Pogson effort.
Park came again with a Ewan Fenley seven-pointer, but for the third time Moseley equalised, this time Santiago Edwards the try-scorer.
Park gained control by the end of the third quarter as Morgan landed two more kicks after Benji Marfo and Joe Luca Smith crossed.
But the hosts salvaged two potentially crucial bonus points thanks to late scores from Sam McNulty and Ethan Priest.
With five games remaining Rosslyn are eight points adrift of third-placed Blackheath, while Moseley on 42 are in the relegation play-off place.
Stortford continue strong form
Bishop’s Stortford moved into the top half of the table with a fourth straight success, leaving hosts Leeds Tykes looking over their shoulder after a 31-19 triumph.
The in-form Hertfordshire men built up a 19-0 half-time lead as Tristan Smith, Austin Pope and Asa Stewart-Harris dotted down, David Hayes with two conversions.
The bonus-point was secured with Alex Rayment crossing, but Leeds showed heart as Lucas Walsh went over before Ed Crossland added to his own score.
Stortford, though, reasserted themselves with Hayes landing after Tom Hitchcock’s try, the efforts of Will Yates and the boot of Crossland not enough for Tykes.
