The Black Cats boss made six changes to the side that had suffered a 4-1 home defeat to Portsmouth last weekend including giving a debut to 18-year-old keeper Ben Alnwick.
"We were outplayed in all areas and outfought in the first half. Our goal put a gloss on the day that our performance didn't deserve but Henry finished us off," he said after the 3-1 defeat at Highbury.
"It was difficult going into that cauldron with an inexperienced team against a very good side.
"We have to make a better fist of it than we did in the first half. It's getting hard for me to keep putting a brave face on things but we have to keep scrapping."