Nadal can tie Federer’s 20 Grand Slams with lucky No. 13 in Paris

Rafael Nadal, right, and Switzerland’s Roger Federer pose with their trophies after the men’s final match for the 2011 French Open tennis tournament at Roland Garros stadium in Paris. Nadal can pull even with Federer for most Grand Slam singles titles won by a man by collecting No. 20 at the French Open, when play begins on Sunday, Sept. 27. (AP Photo/Lionel Cironneau, File)

Rafael Nadal kisses the trophy after winning against compatriot David Ferrer in three sets 6-3, 6-2, 6-3, in the final of the 2013 French Open. (AP Photo/Petr David Josek, File)

For all of the many qualities contributing to Rafael Nadal’s unprecedented superiority at the French Open — the bullwhip of a high-bouncing lefty forehand, the reflex returns, the cover-every-corner athleticism, the endless energy and grit — there’s one element that stands above all the rest.