# ST
my @sorted = map  $_->[1],
             sort { $a->[0] <=> $b->[0] }
             map  [ (split /;/)[0], $_], 
             @lines;

# OM
use Syntax::Construct qw{ // };
my %cache;
my @sorted = sort {
                 $cache{$a} //= (split /;/, $a)[0]
                 <=>
                 $cache{$b} //= (split /;/, $b)[0]
             } @lines;