Pancho's first serve percentage
From a 1957 profile of Pancho Gonzales ("Anyone For Tennis?", New York Times, Allison Danzig):
Francisco (Pancho) Segura, a little South American from Guayaquil, Ecuador, who has the best two-handed forehand the game probably has known, won the Australian professional championship recently. He rates Gonzales the world's No. 1 player, but only because of his service.
Little Pancho goes so far as to declare that big Pancho would not be an outstanding player were it not for his serve. He says that on any surface Rosewall is a better player than Gonzales, except in the service department. "Rosewall," says Segura, "is sounder off the ground. He returns service more consistently and his passing shots are better. Gonzales has more great shots but he is not as reliable. He uses a little too much wrist. He flicks the ball and has no long follow-through."
But no one, Segura concedes, is more consistent than Gonzales in getting his first service into play. When he does, he adds, "You can't attack him. You can't make him work indoors. Outdoors, you can return his service with more length and make him work more to win the points."