If you recall, Democrats were running Andrew Cuomo (Bill Clinton's HUD Secretary) and Carl McCall. Seeing this, Bloomberg ran as a Republican instead. When the Clinton's ultimately endorsed McCall (an African-American), Cuomo dropped out and McCall lost to Bloomberg.Bloomberg wins N.Y. mayor’s race
Political novice defeats Democrat Green in upset to succeed Giuliani
IIRC, Carl McCall was beaten by Pataki the last time Pataki ran.