The catheter has a catheter body and a deflectable section with a flat deflection beam having a different deflection initiation location on each side of the beam to provide nonsymmetrical bi-directional deflection via a single continuous puller wire with two longer parallel segments connected by a U-bend segment anchored at a distal end of the beam. A spacer is provided on each side of the beam to guide and bind the respective puller wire segments and maintain a predetermined separation distance between the puller wire and the beam, including a neutral bending axis of the beam, for reducing the beam's bending moment. One or more heat shrinking tubes may surround the spacer and the beam to tightly constrain the puller wire to the beam.