The solutions is probably to use CSS.
You can use:
p {
font-size: 110%;
}
p + p {
font-size: 100%;
}
That should make the first paragraph larger.
Otherwise, you can use PHP to echo your first <p></p> with a different class:
<p class="firstitem">
This is my first article.
</p>
<p>
This is my second article.
</p>
and use the following in your CSS:
p.firstitem {
font-size: 110%;
}
