A 0-0 draw after extra-time and Krul emerged the hero after saving twice during penalties with the Toon youngsters 2-1 down.
Academy coach Kenny Wharton : "Tim had a thigh strain he picked up in the second half and he was hobbling a bit. I was concerned that if the ball came back to him and he had to kick it might go.
"I missed the last round against Stoke because I was having a nose operation, but I heard he was good and he was super confident again. After the extra time had finished, I read out the first five penalty takers and Tim said he wanted to be the sixth!
"He was ready to take a pen if needed.
"I wasn't going to use all of our subs just in case Tim got injured. We have a young keeper in Fraser Forster on the bench who is 6ft 7in. I was going to throw him on as an outfield player to then put in goal if Tim's thigh went. But in the end it worked out fine."
NUFC: Krul, Cowan, Deverdics (Morris 82mins), Marr, Huntington, Cavener, LuaLua (Little 87mins), Doninger (Godsmark 100mins), Carroll, Troisi, Critchlow. Subs Not Used: Reay, Forster.