The Reds cruised into a 2-0 lead at half-time, with Lallana adding to Daniel Sturridge‘s opener with a superb strike in front of the Kop.
Goals from Papiss Cisse and Jack Colback turned the game on its head in the second-half, however, with any slight top-four hopes going up in smoke for Liverpool.
“We’ve set our standards high in the last couple of months, we’ve been on a great run, and I think that’s why I’m so disappointed for the lads that we’ve not managed to keep that going with another three points,” Lallana said post-match.
“[We’re] very frustrated. It was such a positive performance first half and we said at half-time we needed to come out fighting because they’re scrapping for every point.
“I feel we took our foot off the gas a little bit, lost momentum, and credit to Newcastle, they probably got a deserved point in the end.
“But it is what it is, and we’ll recover now and head to Villarreal.”
“We want to win every game, whether it’s the league or the Europa League,” he added.
“The manager has made changes to keep everyone fresh but we’ve proved we’re good enough to get three points regardless of the team he puts out.
“It’s disappointing, but we’ve got a big game to look forward to now on Thursday.”
A ruthlessness is required against the La Liga side, or Klopp and his men will find themselves in trouble heading into the second-leg at Anfield a week later.