template programming: ambiguous call to overloaded function

I am implementing a sorting algorithm as personal training (no homework!). I have the following code (excluding imports etc.):

        template<class RandomIt, class Compare>
        void sort(RandomIt first, RandomIt last, Compare comp)
        {
            /* actual sorting code is here */
        }

        template<class RandomIt>
        void sort(RandomIt first, RandomIt last)
        {
            std::function<bool(decltype(*first), decltype(*last))> comp = [](decltype(*first) a, decltype(*last) b)
            {
                return a < b;
            };

            sort (first, last, comp);
        }

Trying to call this code with a test array

    auto test_array_1 = std::make_unique <std::array < uint64_t,SORTING_TEST_LENGTH >> ();
    std::copy(std::cbegin(*template_array), std::cend(*template_array), std::begin(*test_array_1));

    sort(std::begin(*test_array_1), std::end(*test_array_1));

The compiler complains about "ambiguous call to overloaded function" (VC++ C2668). From my understanding the call should not be ambiguous though. Also giving the call in the second sort function the template parameters for the first sort function does not have any effect.

What am I missing here?