The Mexico striker - in the side for the injured Wayne Rooney - netted the decisive goal in a 4-3 victory over Newcastle on what was just his fourth league start this season.
An anticipated three-week absence for Rooney should mean further opportunities for Hernandez, who has now scored four late winners in little more than two months.
He said: "Ask any player in the world and they will tell you they want to play every game. But the competition here is incredible.
"It is the biggest club in the world. You need to be aware there are five strikers who want to be part of the games. I have to prove, in one minute or 90, that I want to start."
Hernandez now has 10 goals in all competitions, though two good chances went begging before his luck turned on Wednesday.
He said: "You cannot afford to regret every chance you miss because if you do you will never be concentrated for the next opportunity.
"You are never going to play the perfect game. You will never score five goals from five opportunities. That is the beauty of football."