Según (Spanish for “according to…”) comes from the Latin secundum, meaning the same. Secundum itself comes from the Latin… sequor, meaning, “to follow” — just like the Spanish for the same, seguir!
Thus, we can see in all these variations, not only the s‑g-r or s‑c-r root (the g/c are easily and often interchanged!) but also the commonality with the English… second, that also comes from the same origin.
Second, after all, follows the first.