wp_restore_post_revision( int|WP_Post $revision_id, array $fields = null )

function wp_restore_post_revision( $revision_id, $fields = null ) {
	if ( !$revision = wp_get_post_revision( $revision_id, ARRAY_A ) )
		return $revision;

	if ( !is_array( $fields ) )
		$fields = array_keys( _wp_post_revision_fields( $revision ) );

	$update = array();
	foreach ( array_intersect( array_keys( $revision ), $fields ) as $field ) {
		$update[$field] = $revision[$field];
	}

	if ( !$update )
		return false;

	$update['ID'] = $revision['post_parent'];

	$update = wp_slash( $update ); //since data is from db

	$post_id = wp_update_post( $update );
	if ( ! $post_id || is_wp_error( $post_id ) )
		return $post_id;

	// Update last edit user
	update_post_meta( $post_id, '_edit_last', get_current_user_id() );

	/**
	 * Fires after a post revision has been restored.
	 *
	 * @since WP-2.6.0
	 *
	 * @param int $post_id     Post ID.
	 * @param int $revision_id Post revision ID.
	 */
	do_action( 'wp_restore_post_revision', $post_id, $revision['ID'] );

	return $post_id;
}