The summer signing from Swindon marked only his second league start of the campaign with a man-of-the-match performance and a stunning goal in the 5-0 victory over Hornets.
Cox is now hoping to keep his place in the side for next weekend's game with Leicester City after feeling he has proved a point that he can make the step up to the Championship.
"It's been hard but I have just had to work hard and bide my time - and I was happy to do so," said Cox.
"But when you feel you've got a point to prove, it's nice just to get out there and play.
"If you can score a goal it's even better
"I've been working hard in training and trying to score as many goals as I can and when you get your chance you have to take it.
"I went out to enjoy myself and relax and enjoy the whole occasion and hopefully get on the scoresheet, which I did in the end.
"Confidence now is high and I just hope now that I can build on the goal that I have scored."