It is not often that N.F.L. apparel provides a clue of a spectator’s allegiance to a tennis player. But as play at the U.S. Open began Monday morning on Court 7, several fans in Buffalo Bills attire rallied around the 21-year-old qualifier Jessica Pegula as she sought her first victory in the main draw of a Grand Slam event.

Pegula, who won by 6-3, 7-5 against the French Open quarterfinalist Alison Van Uytvanck, is the daughter of Terry Pegula, the oil and gas mogul who owns the Bills and the N.H.L.’s Sabres. That connection has provided her with a support structure that players in her strata of the rankings — she is currently No. 260 — rarely get.

The Bills also provided a welcome diversion for Jessica Pegula as she recovered from a knee operation that kept her out of competition for nearly a year.