The Raiders came out of the locker room and played like last year's state finalists, but after the first quarter Winchester dominated the boards and stopped Watertown's top scorer, Patrick McHugh, on the way to a 58-45 win for the visitors.
Senior captain McHugh scored 9 of the Raiders' 11 first quarter points, and Watertown led by three after one period. He scored four more early in the second, but the Sachems battled back to end the half on a 12-2 run, giving Winchester a 21-17 lead at the half.
Senior Craig Fitzgerald capped the first half for Winchester by hitting a two pointer and drained the free throw after being fouled on the shot. He was just getting started, as he scored 14 second half points to help the Sachems pull away from Watertown.
McHugh, on the other hand, cooled off in the second half, scoring just 2 points late in the game when the outcome was not in doubt. He finished with 15 points.
Winchester was also aided by junior Ryan Murphy's 11 points and senior Conor Dunleavy's 9 points.
No other Raider scored in double figures, with junior Joey Farrar scoring second most with 7 points on the night. The Raiders dropped to 0-3 after losing to Belmont by three and Arlington by 2 on the road.