Apply CSS rule to only the first <td> in <tr>'s WITHOUT assigning a class/id?

I have already viewed this, it's not what I need here..

I need something like

table.mytable tr first-td's { border: 1px solid black; }

for

<table class="mytable">
<tr>
<td>This has the border</td>
<td>no border</td>
<td>no border</td>
</tr>
<tr>
<td>This has the border</td>
<td>no border</td>
<td>no border</td>
</tr>
<tr>
<td>This has the border</td>
<td>no border</td>
<td>no border</td>
</tr>
</table>

If this is impossible just let me know and I'll be sad.

Javascript/jQuery is acceptable if it's needed to get the job done.