Newcastle boss Alan Pardew has admitted that poor defending allowed his side to be ambushed by Fulham.
Newcastle relinquished their 1-0 lead as Clint Dempsey scored three of Fulham's five goals in a dramatic second-half turnaround.
"We felt we had the game won. We were so dominant in the first half and perhaps we should have led the game by more," Pardew told the BBC.
"But we didn't defend well and that's been the key to our success this year."
He added: "We took our foot off the pedal and were caught out by some poor goals.
"But they needed a break and the first goal looked very soft to me. The penalty gave them a lift but I don't quite know why we switched off like we did for the next five or 10 minutes. That was the disappointing part of the game for us."
Newcastle were without Demba Ba, Cheick Tiote and new signing Papiss Demba Cisse - all on Africa Cup of Nations duty - but Pardew doesn't believe his side missed them.
"That certainly wasn't a problem in the first half and it shouldn't have been a problem in the second," said Pardew
"We have had a terrific season and we have to make sure that kind of period never happens to us again."
Meanwhile Fulham manager Martin Jol believes his tactical changes provided his side with the platform to launch a comeback.
"We didn't do the right things in a 4-3-3 formation and never looked threatening," Jol said.
"The first half was awful, but the second half was fantastic.
"We made the changes [bringing on Andy Johnson and Chris Baird]. I am happy with myself that I made these changes because luckily it paid off for us."
Dempsey, the first American to score a hat-trick in the Premier League, was satisfied with an important win.
"The second half had to get better because it couldn't have been worse than the first half," Dempsey told the BBC.
"Luckily the ball kept going in. We never took our foot off the gas and took our chances."