The second-half dismissal of fellow American goalkeeper Brad Friedel meant Guzan had to come off the bench for his first league appearance.
The former Chivas USA keeper told AVTV: "It's exciting to make my Premier League debut but under the circumstances I would have wished for it to have been a bit different.
"Any time you have to face a penalty is difficult let alone when coming off the bench.
"But in those circumstances you try and do your best and unfortunately I couldn't keep it out of the back of the net. So that part stings a bit but we are all just going to want to put this behind us.
"I don't think we were at our best and obviously when you play big teams in big games you have to be good and be ready to play from the start."