A tissue puncture access assembly that includes a sheath and a dilator. The sheath is operable between an expanded position with a first maximum outer diameter, and a collapsed position with a second maximum outer diameter that is less than the first maximum outer diameter. The dilator is insertable through the sheath and has a leading end positionable distal of a distal end of the sheath. The sheath is operated into the collapsed position prior to and during insertion with the dilator into a tissue puncture. The sheath is operated into the expanded position once positioned in the tissue puncture.