WILSON US OpenxDuty Tennis Balls For more than 40 years, every point at the US Open has been scored with a WILSON US Open tennis ball. Unparalleled consistency & performance make it the gold standard in tennis, trusted by the best in the game when it's all on the line. Crafted with premium woven felt for superior bounce characteristics over the course of three sets, this ball is available in Extra Duty, Regular Duty & High Altitude variations to ensure optimal performance on your preferred playing surface.