Cold, wet conditions stripped Friday's game of any colour with six of the seven tries scored from close range in a match dominated by the packs.
It was good enough for the Crusaders to put losses to the Highlanders and Hurricanes behind them, a rare double setback after marching through 2017 with only one loss.
The Bulls slumped to a fourth-straight defeat, paying the price for their lack of clinical finishing, having edged the hosts in territory and possession.
The Crusaders led by a flattering 21-7 scoreline at halftime.