Jacob Sharff and Jeremy Boyd were at opposite ends of the Billie Jean King National Tennis Center in Queens on Wednesday when a chair umpire’s voice crackled over their two-way radios: “Wheelchair tech needed on Court 13.”

In less than a minute the two men, in wheelchairs themselves, converged on the court to discover that a small caster wheel had come loose on Daniel Caverzaschi’s chair. The technicians had 15 minutes to fix it or Mr. Caverzaschi, a Spanish player, would be disqualified from the match.

Mr. Sharff slid from his chair onto the court, and the two men repaired the wheel in just seconds. Play resumed.

Mr. Sharff, Mr. Boyd and a third technician named Mike Sheen are the trio of specialists who make up a kind of tennis pit crew, responsible for quickly repairing any wheelchairs that break at the U.S. Open.

Quickness is key. Calls are rare, perhaps one a day, but if the problem cannot be fixed in the allotted 15 minutes, the player is disqualified.

All day, they patrol the courts, spreading out over the grounds to maximize their coverage, waiting to spring into action.