Abstract: An automotive vehicle door 10 having a window panel 22 movable to close and partially open a window opening 18 is stabilized against lateral movement when in a partially open position by a lower channel 28, mounted substantially below a beltline section 32 of the window opening 18, which has a narrowed width section 64 with sides 46 inwardly crimped along a longitudinal axis thereof for cooperating with a deformable glass run 66 mounted within the lower channel 28 to restrict inboard and outboard movement of the window panel 22. A sleeve 52 between the lower channel 28 and a middle channel 26 limits relative lateral movement therebetween, and a reinforced window seal 36 along the beltline section 32 of the door 10 provides further lateral support for the window panel 22 in the partially opened position.