Obviously...but before that?
I could be wrong. But I think the answer is never. I've looked and seen a #4 and #5 but never a #1.
EMU and WMU had some pretty good teams back in the day.
But if it is the first, MAC office should be all over that.
Should.
I think it's a very interesting question. I checked a couple of media guides just out of curiosity. Ohio basketball's media guide lists games against ranked opponents (since 1960). During that time, Ohio is 0-6 against #1's (last one was against UC in 1999). Ohio football media guide does not list those games. However, the 2010 game notes included record vs. ranked opponents since 1990. During that time, Ohio hasn't played a #1.
I checked Miami's guide and they do note their wins vs. highest-ranked opponents. In football, they beat #8 LSU in 1986. And in hoops they've beaten the #6 team twice (Utah in 1999 and UNC in 1973).
Other than tweet volume, the MAC Media Relations guys are not that strong. Of course, maybe it's a double-edged sword. Maybe you don't want the world to know that none of your teams have beat a #1.