Javi Gracia replaced young forward Othmane Maamma at half-time against Sheffield Wednesday to avoid the possibility of him being sent off, the Watford head coach revealed.
The 20-year-old Moroccan, making only fifth league start for the club, was shown a yellow card in the 11th minute at Hillsborough for a foul on Harry Amass.
But he was afterwards one of Watford's main threats in attack, forcing a good save from the Wednesday keeper and providing an assist for Imran Louza to shoot following a weaving run.
"Before half-time, the other bench was pressing the referee to give the second yellow card," Gracia told BBC Three Counties Radio.