Rosette led the contest through Dean Bryerley's goal from a JP Watson cross.
But Johnny McGough's Pier Reserves side battled back to dominate the clash, Brad Marshall smashing in four goals and Rob Whitehead a hat-trick as they romped to an 8-4 win.
Pier led 5-1 at the break and despite Rosette hitting back through late goals from Si McDonald and Dane Robinson, man of the match Jake Adams added another for Pier, who took the three points.
The game was marred late on as Rosette's Robinson suffered what appeared to be a bad injury to his knee ligaments.
A depleted Rosette side battled throughout the contest, with nobody in particular standing out.
Snainton closed the gap to third-placed Goldsborough United, whose game against Ayton was postponed, as they drew 2-2 with Eastfield Athletic.
Ryan Collings hit both of Snainton's goals, while Tyler Whitton was their man of the match.
Paul Oldroyd fired in both of Athletic’s goals, his second a last-gasp equaliser to seal a point for his side.
Athletic’s entire team impressed as they battled to take a share of the spoils.
Cayton Athletic have a chance of mounting a late surge for one of the three promotion places available after they beat Eastfield Town 3-1.
Freddie Schmuck scored a superb solo goal to hand Athletic the lead, before a Ryan Somers free-kick made it 2-0.
Player-boss Macauley Youngson headed his side into a 3-0 lead from Schmuck's free-kick to end the contest.
Eastfield netted a late consolation, but Athletic had done enough to claim the win.
Makeshift centre-back Michael Hernandez was Athletic's man of the match.
Seamer Reserves sealed a 2-0 win against Newlands Reserves.
Paul Greatorex's men scored both their goals in the first half, man of the match Dan Jewitt's back-post header opening the scoring before Ollie Parker latched onto Mike McNaughton's through-ball to double their advantage.
Newlands' man of the match was Ben Reedie.
Edgehill Reserves v Fishburn Park Reserves was postponed.
DON'T MISS!! 25 OF OUR OLD SATURDAY LEAGUE TEAM PICS / https://www.thescarboroughnews.co.uk/sport/football/photo-focus-do-you-recognise-these-25-saturday-league-team-pictures-1-9579084
DIVISION 2 Eastfield Town 1-3 Cayton, Edgehill Reserves P-P Fishburn Park, Goldsborough P-P Ayton, Seamer Reserves 2-0 Newlands Reserves, Snainton 2-2 Eastfield Athletic, West Pier Reserves 8-4 FC Rosette