This should do it, although I'm not sure if reading the input file in one slurp scales well to very large files. You did say the fields are separated by a space and a comma? A comma followed by a space seems more likely; if that's the case the regexes should be changed to
/^(.*?), /
If the first field is not numeric on a line, you will get warnings (if they're turned on), but it will finish, and sort them first in the output.

#!/usr/bin/perl -w
use strict;

my @whole_file = <>;
my @new_array = sort by_first_field @whole_file;
print @new_array;

sub by_first_field {
  $a =~ /^(.*?) ,/;
  my $x = $1;
  $b =~ /^(.*?) ,/;
  my $y = $1;
  return $x <=> $y;
}
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This sorts according to the comparison defined in the subroutine "by_first_field". $x and $y are set to the captured data in the regexes, and a return value is generated by using the numeric sort operator <=> (aka the spaceship operator). See chapter 15 in Learning Perl for more info.

TheEnigma