NEW YORK—Tommy Paul kicked off his 2024 US Open preparation after reuniting with his No. 1 fan on Arthur Ashe Stadium. The tournament’s social media team was on hand to capture the moment.

FRISCO, Texas—Reilly Opelka and Tommy Paul grew up training together, roomed together in junior dorms, even shared a house together as established pros. Oddly, despite playing more than 500 combined ...