NEW YORK — A year ago, Carlos Alcaraz showed up at the Billie Jean King National Tennis Center with a buzz cut and a rocketing serve, unlike any arrow he had ever had in his quiver before. He lost three service games in seven matches, and won the U.S. Open men’s title. No one ever had a chance. This year, he has shaggy mane and uses a thin headband to keep it all under control, plus a serve that is nowhere near as potent as it was 12 months ago. That’s OK. In the absence of the 132 mph blasts and the sidewinding aces, a subtler but no less devastating arrow is doing its work. A player...