Despite missing three of four from the foul line in the final 23 seconds, the Pioneers (1-2) held on for the three-point comeback win.
Junior Matt Rucker (Proctorville/Chesepeake) broke a 109-109 tie by nailing two free throws with 45 seconds left on the clock to give Marietta the lead for good.
The Bison (1-2) led by as many as 10 points during the first half, but Marietta used a 15-to-7 run over the final four minutes to pull within two points, 53-51, at intermission.
Neither team could build much of advantage in the second half, but Bethany managed to hold a 107-100 lead with 3:54 remaining in the game. Marietta, however, closed the game on a 12-2 run to steal the victory.
Marietta out rebounded Bethany 51-41, including 27-11 on the offensive end.
Rucker led the Pioneers, who shot 39-of-91 (.429) from the field and 15-of-47 (.319) from long range, with 23 points and seven rebounds in 14 minutes.
Junior Chad Sponseller (Canton/GlenOak) hit five three-pointers and finished with 20 points and three assists.
Junior Ryan Wilkinson (Wilmington/Clinton Massie) added 13 points and four assists, while sophomore Craig Stewart (Circleville) finished with 11 points and three steals.
Bethany shot 44-of-73 (.603) from the floor and out scored Marietta 21-19 at the line, but did not connect on any of its seven three-point attempts. The Bison were paced by Mike Drahos with 33 points and nine rebounds, while teammates James Wallace and Matt Drahos added 22 and 21 points, respectively.
The Pioneers will look to even their record Saturday (Nov. 26) when they take on visiting Kenyon in the second game of a OAC vs. NCAC Challenge doubleheader on Fenton Court. Muskingum will take on Denison at 1 p.m. and Marietta will follow against Kenyon at 3 p.m.