Has the basketball team ever just had one loss going in to MAC play ?
That's kind of a tricky question, as MAC play has started in early December in the past. But I know what you mean, and the answer is yes: 69-70. That was the famous "Ohio Wins the Big Ten" year when they went 9-1, with the only loss coming on a neutral floor against Texas. That squad was 20-5 (9-1) overall. They lost to Notre Dame and Austin Carr in the NCAA Tournament; OCF would love to relive that.
The Elite Eight team had two losses before MAC play.
The 54-55 team was 3-0 before MAC play, though those wins were against Marietta (played them home-and-home that season!), Morris Harvey, and Ohio Wesleyan (road). The 53-54 team was 3-1. Go back much further than that and you're getting into independent, BAA, and OAC years.