I’m assuming that you’re talking about the “home page” when you say “1st page only”. Or are you talking about the first “paginated” page of your posts? If its the prior, you’d probably want to use the “is_front_page()” conditional if you’re using a single page.php template.
Or maybe it’d be easier to make a “page-home.php” template and do some sort of new query of your posts…just for that page. Would that work?