Krul was sent up for a last-gasp corner as the Magpies pushed for an equaliser, when his shot was blocked in a crowded area, only for referee Howard Webb to blow for full-time instead of a penalty and send Newcastle north with no reward for a battling display.
"In my opinion it was a penalty," said Krul. "I controlled it on my chest and his arms were up in the air. Sometimes it's difficult for the referee to see it but that's when you need his assistants to help him a little bit and unfortunately it didn't fall for us.
"He told us it was very close and he thought his hands were by his side, but they weren't. His arms were up in the air and in my opinion it was a penalty."
Fulham almost scored midway through the second half when Johnny Heitinga's deflected shot crashed against the underside of Krul's bar and appeared to have bounced over the line, only for goal-line technology to show a tiny section of the ball was on the line.
Cauley Woodrow then followed up to bundle home only to be flagged offside.
"We got lucky in that instance," added Krul. "I didn't know where the ball was after it hit the crossbar and we were lucky that the linesman made a great decision.
"We trust the technology and the referee in that. So that's a huge help."
Krul refused to blame Alan Pardew's stadium ban for Newcastle's defeat.
"It's not the same without the manager on the side because he gives you the extra confidence and maybe a little bit of help, but he did everything in his power to help us," he added.
"We had a team meeting at the hotel and then he rang John Carver at half-time to give him some instructions. It didn't affect the team, we just had to take our chances and we didn't today."