It actually started during the Spurs series after SA had won G1. The Spurs announcers said it. After the Bullets when up 3-1, Motta used it and gave credit to the Spurs announcers when using it. He said it again up 3-1 against the Sixers and that is when it got really hot.
This is my favorite memory from that season as a big Bullets fan. You don't see this kind of musical talent these days: