Improved methods for percutaneously creating, entering and/or dilating an opening in the wall of a blood vessel or other anatomic structure. The improvement comprises deploying a guide element having a proximal segment and a distal segment, the diameter of said distal segment being greater than the diameter of said proximal segment at their juncture, and which at said juncture forms an abrupt circumferential step comprising a proximally-facing surface. Said proximally-facing surface abuts the catheter's tip and shields said tip, thereby facilitating passage of said catheter as it enters and passes through said opening in said wall of a blood vessel or other anatomic structure.