It was a little over eight years ago (January 27, 2011). The Michigan team limped into the Breslin with an 11-9 overall record, 1-6 in Big Ten play. At this point, John Beilein was 57-62 as Michigan's coach, and 23-39 (!) in league competition.
At that point, the Michigan basketball program had made the NCAA Tournament once since 1998; it had not reached the Sweet 16 since 1994; it had not reached the Final Four since 1993; and it had not won the Big Ten since 1986. If you were a college student in 2011 you probably had no actual memory of Michigan ever being good at basketball (and some of the games you might have remembered were vacated by the NCAA).
Entering that 2011 game, Michigan also had not beaten MSU on the road in the 21st century (last time had been 1997) and hadn't beaten them at all in Beilein's tenure. MSU incidentally was coming off back-to-back Final Fours.
From that game onward, Beilein is 213-83 overall, 100-50 in Big Ten play, 17-7 in the NCAA Tournament and has won two Big Ten titles, two Big Ten Tournament titles, reached the Sweet 16 four times, and the national championship game twice.
It's rare that you can find this clear of a watershed moment for a coach/program.