Spaniard Sainz was handed a 10-place grid penalty through no fault of his own after a metal drain cover came loose and wrecked his speeding car when it drove over it, forcing the cancellation of opening practice.
Former F1 racer Warwick was one of the four stewards at the November 18th night race.
"It's a difficult job for a steward, the same as a referee, and we've got to be impartial, we've got to be strict and we've got to be hard sometimes even when it hurts us," the Briton said at the Autosport Awards in London on Sunday night.
"The penalty we had to give Sainz in Vegas, it felt wrong, it was wrong, we worked very hard for it not to happen but they're the rules."
The stewards noted at the time that they would have granted a derogation due to 'mitigating, unusual and unfortunate circumstances' if they could have done but there was no provision in the rules.
Sainz triggered an automatic penalty when Ferrari were forced to replace his car's energy store, exceeding his quota of two for the season.
