Court 5 at the United States Open overflowed with spectators on Monday, many standing on their tiptoes, craning their necks and waiting in lines at the small side court to get a glimpse of a teenager who holds some hope for the future of American men’s tennis.

Zachary Svajda is only 16, but until full-body cramps overtook him early in the third set against the veteran Paolo Lorenzi, he was the better player. Ultimately, Svajda could barely serve because of the cramping, and he was reduced to limping across the court. Lorenzi came back to win, 3-6, 6-7 (5), 6-4, 7-6 (4), 6-2, in 4 hours 20 minutes, much to the dismay of the oversize crowd.

“For sure, he is much better than I was at age 16,” the 37-year-old Lorenzi said.

Svajda, who is from San Diego, was one of three young American men who impressed on Monday, alongside Reilly Opelka and Jenson Brooksby.

Opelka, 21, scored one of the upsets of the day, beating No. 11 Fabio Fognini, 6-3, 6-4, 6-7 (6), 6-3, on Court 17 .