The January 20th, 1990 Georgetown game at the HCC still ranks at the top of all the live events I have ever witnessed. I often see people mention the Syracuse game from the Monday 5 days earlier in the same sentence/paragraph. I was at both games, one in the stands ('Cuse) and the other (G'town) on the floor doing color on WHUS. And I can unequivocally state that the electricity in the building at the Georgetown game was of an order of magnitude greater than anything I had ever felt, even for the Syracuse game 5 days earlier. At 12-0 when John Thompson called his 2nd TO you could not even hear yourself think. John Tuite and I looked at each other in utter amazement. And as others have pointed out in previous threads on this very topic (Matrim, Mau, etc...) it got even louder in the waning minutes as we salted the game away.
The biggest reason why was simple... we had beaten Syracuse several times over the previous few years, and it was already a widely-held belief that you could beat Boeheim's teams because they tended to be a bit too loose at times. But beating the big, bad Hoyas and John Thompson was a totally different animal. They had tortured us for years, and even when we got close a couple of times (who could forget the game in January 1988 of the 1987-1988 at the Capital Centre where Alonzo literally shoved Tate George into the stanchion under the hoop with less than a minute to play and then got a gimme putback with no call by the obviously-blind baseline ref) we almost always lost to them.
And of course beating them on that Saturday night in 1990 kept them from assuming the #1 ranking that was theirs for the taking after Kansas lost earlier in the day. That game was the true mark of when you could really feel something truly magical starting to happen with that team... and, as it turns out, for the program as a whole.