Cortland rebounded and McMahon hit a pair of free throws with two seconds left to seal it.
Mikey McElroy had 15 points for O-State, which received respective 11- and 10-point nights from Jack Dignan and Zuvic.
Lee had five points and seven assists for O-State, which will host Brockport at 8 p.m. Friday.
Hartwick senior Jared Suderley was named to the D3hoops.com Team of the Week, one day after the Empire 8 Conference selected him as its Player of the Week.
Suderley led the Hawks to a 3-0 week, shooting 53 percent from the field in wins over Stevens, Alfred and Houghton.
Against Houghton, Suderley scored his season high of 36 points and also grabbed 17 rebounds.