Paris, June 10 -- For a few, fleeting moments Sunday, Rafael Nadal found his French Open supremacy seemingly threatened by Dominic Thiem, a younger, talented opponent challenging him in the final for the second consecutive year.

A poor game from Nadal allowed Thiem to break him and even things at a set apiece. That development brought fans to their feet in Court Philippe Chatrier, roaring and clapping and, above all, wondering: Was this, now, a real contest? Could Thiem push Nadal more? Could Thiem make this surge last? Would Nadal falter?

That the questions arose at all was significant. The answers arrived swiftly. Nadal reasserted himself, as he usually does at Roland Garros, by grabbing 16 of the next 17 points and 12 of the remainin...