Magento 2 How to get First Item from getList()?

Try this way:

$searchCriteriaBuilder->setFilterGroups([$filterGroup]);
$searchCriteria = $searchCriteriaBuilder->create();
$searchCriteria->setPageSize(1)
               ->setCurrentPage(1);

$productList = $this->productRepository->getList($searchCriteria);
$item = current($productList->getItems());