You can make a blast database of your sequences with the makeblastdb command (in linux):

makeblastdb -in genomesORFs.fas -dbtype nucl -out my_db

Then blast your sequences against it with a command like this, but choose your own parameters (there's loads on info at sites like this and this:

blastall -p blastp -i my_input_file -d my_db -o my_output_file -m 8

You can run it through a perl script to print the best match for whatever parameter you want. Something like this pulled from a different script (NOT THIS):

#!/usr/bin/perl
use strict;
use warnings;

my $BLASTn_file = $ARGV[0] ;

open BLAST, "< $BLASTn_file or die("$BLASTn_file\n$!");
while (my $line = <BLAST>){
    if ( $line !~ /^#/ ) {
            chomp $line;

            my @fields = split(/\t/, $line);
            my $query = $fields[0];
            my $match = $fields[1];
            my $evalue = $fields[10];

            if ((not exists  $Match{$query}) or ($evalue <  $Evalue{$query})){
            # Select lowest eval
                    $Match{$query} = $match;
                    $Evalue{$query} = $evalue;
            }
    }
}

   while (my ($key, $value) = each (%Match)) {
        print "$key\t$value";
  }