Argument expansion with format command

I came across a scenario, where I need to use the argument expansion with format command. With Tcl8.5, I am using {*} and it works like charm.

But, with Tcl8.4, i have tried eval. But, no luck.

% set x "This is stackoverflow"
This is stackoverflow
% format "%10s %5s %20s" {*}$x
      This    is        stackoverflow
% eval format "%10s %5s %20s" $x
   %5s
% eval list format "%10s %5s %20s" $x
format %10s %5s %20s This is stackoverflow
% eval [list format "%10s %5s %20s" $x]
not enough arguments for all format specifiers
% eval format "%10s %5s %20s" [list $x]
       %5s
% eval format "%10s %5s %20s" [concat $x]
       %5s

What is my mistake here ?