Patrick Ostermann made 32 saves as Nelson stunned the division-leading Beaver Valley Nitehawks 2-1 on Tuesday.
Blair Andrews scored both goals for the Leafs (19-25-2), who moved within four points of third-place Grand Forks.
Sam Swanson had the lone goal for the Nitehawks (31-10-6), while goaltender Brett Clark stopped 28 shots.
(CORRECTION: Due to an error on the KIJHL website, an earlier version of this story stated that Josh Williams played in net for Nelson.)