Change function to only pull from one category

This code is hooked beneath each post. It displays the thumbnail and title of 4 posts from the same category as the preceding post.

It works as long as the post is only assigned to one category, but if it is in two it shows 4 posts from each category (thus totaling 8).

How would I change this function to only include the 4 posts from one category? I don’t care which of the 2 categories, it could just choose the first one, or it could exclude by category slug or ID….

/** You may also like */
function my_related_posts() {
if (is_single()) {
	global $post;
	$current_post = $post->ID;
	$categories = get_the_category();
foreach ($categories as $category) :
	?>
<div class="featured-posts-box"><div class="my-recent-posts"><h4>More articles in <span style="font-style:italic;color:#a5d2d8;"><?php
$category = get_the_category();
echo $category[0]->cat_name;
?></span></h4><ul class="top-featured-image">
	<?php
	$posts = get_posts('numberposts=4&orderby=rand&category='. $category->term_id . '&exclude=' . $current_post);
foreach($posts as $post) :
	?>
<li  class="top-featured-image"><span><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></span> <?php if ( has_post_thumbnail()) : the_post_thumbnail('thumbnail'); endif; ?></li>
	<?php endforeach; ?><?php endforeach; ?>
</ul>
</div>
</div>
	<?php
		}
	wp_reset_query();
}