if(!function_exists('woo_discount_rules_price_strikeout_display_only_discounted_price')){
    function woo_discount_rules_price_strikeout_display_only_discounted_price($item_price, $product){
	$item_price = preg_replace('/<del>.*<\/del>/', '', $item_price);
        return $item_price;
    }
}

add_filter('woo_discount_rules_price_strikeout_after_discount_price', 'woo_discount_rules_price_strikeout_display_only_discounted_price', 10, 2);