Maggie Hall assisted on Siver’s goal, which came on a 15-yard shot to the left corner that beat MM goalie Michaela Carnegie (12 saves).
Katie Kleban made 18 saves in the shutout for Cooperstown (6-1, 3-1), which was outshot, 23-18.
Cooperstown hosts Little Falls on Saturday.
Sidney 4, Deposit 1
Nicole Smith had a goal and an assist to lead visiting Sidney to a Section Four victory.
“We had great passing to spread the field and develop terrific scoring opportunities in the circle,” said Sidney coach Christine Race, whose team earned double-assists on goals by Smith and Bre Voltz.
Mallory Stillman and Hannah Wood also scored for the Warriors (4-3, 3-1), who got three assists from Dawn Savino.
Kelsey Decker stopped seven shots in goal for Sidney, which visits Deposit (5-3) on Monday.
Afton 3, Walton 1
Karli Conpropst scored on a double-assist from Ashley Rogalski and Bailey Sherman five minutes into the second half, snapping a 1-all tie to lead Afton to a Section Four victory on the road.
Sam Rogalski scored inside the first minute for the Crimson Knights (7-4, 6-0), who gave up a goal to Jamie Budine seven minutes later as the teams headed into halftime tied at 1.
Conpropst and Hanna King scored in the second half for Afton, which finished with advantages of 29-3 advantage in shots and 21-2 in penalty corners.
Emily Bartlett stopped 14 shots for the Warriors (2-6, 1-4), who host Tioga for a non-division game at 10 a.m. Saturday.
at Sidney CC
Trever Dutton earned medalist honors with a 5-over-par 41 on the front nine of the Sidney Country Club, leading host Sidney to its sixth victory of the season.
Cameron Luca shot a team-low 46 for Bainbridge-Guilford.
Jon Gorshack and Kyle Smith each shot 44s for Sidney (6-2), which will visit Chenango Valley State Park on Thursday for the Midstate Athletic Conference Championships.