list_x = [(1, 1), (1, 2), (2, 3), (2, 5), (4, 6)]
list_y = [(1, 1, 33), (1, 3, 65), (2, 4, 11)]
for elx in list_x:
    for ely in list_y:
        if ely[:-1] == elx:
            list_y.remove(ely)
print(list_y)
[(1, 3, 65), (2, 4, 11)]
Python: Compare 2 lists of tuples of different size