The invention concerns a telescoping strut (1) for a retractable landing gear (LG) in an aircraft (A). The telescoping strut (1) comprises a pre-pressurized and central extension chamber (12) extending along the telescoping strut (1) and a surrounding retraction chamber (13). For retraction, an hydraulic generation architecture (HG) of the aircraft (A) feeds a single input / output passage (24) of the surrounding retraction chamber (13) with a overcoming fluid pressure that overwhelms a extension positive pressure in the central extension chamber (12) and opposes the effect of the pre-pressurizing. The retraction system (S) is for instance for a rotorcraft.