Just read the documentation for open and for sysopen. As they are different, the difference in content will likely be the difference in operation.

You'll learn not only the answer but also an approach to similar questions from this:

perldoc -f open
perldoc -f sysopen
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perlopentut says

If you want the convenience of the shell, then Perl's open is definitely the way to go. On the other hand, if you want finer precision than C's simplistic fopen(3S) provides you should look to Perl's sysopen, which is a direct hook into the open(2) system call. That does mean it's a bit more involved, but that's the price of precision.

As stated before sysopen comes with more precision than open.

sysopen helps avoiding race-conditions.

Consider the following snippet:

if (-e $file) {
        open(FH,">","$file") or die $!;
}
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It's a two step process:

1. File test
2. open

sysopen needs only one step (kind a simplistic, but you should get the message).

use Fcntl;

sysopen(FH, $file, O_WRONLY|O_TRUNC|O_CREAT, 0600)
        or die $!;
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HTH,
Thomas