They had some heavy fighting outside Basra...heavy for the targets, anyway.
With Basra itself, they basically parked outside and spent a week or two inflitrating in, learning who was what, securing the co-operation of friendly civil figures, extensively using sniper teams to kill every Baath figure they could spot co-ordinating any resistance, and then drove in in force.
The groundwork beforehand meant that resistance was close to non-existent.