Liverpool dominated the first half against an injury-hit Leicester and looked set to take a deserved lead when they were awarded a 16th-minute penalty, only for Egyptian Mohamed Salah to see his spot kick saved by home goalkeeper Kasper Schmeichel.
The chances kept coming for the visitors, with Sadio Mane blazing over when he should have scored early in the second half.
Liverpool's profligacy proved costly as Lookman fired Leicester in front just before the hour mark, sparking scenes of euphoria at the King Power Stadium.
It was backs to the wall for Leicester after that, but they dug in to secure a win that leaves second-placed Liverpool six points adrift of leaders Manchester City, as Foxes coach Brendan Rodgers got one over on the side he used to manage.
"It was not our plan tonight to give City the chance to run away," Klopp told reporters. "If we play like tonight we do not think about catching up with City.
"But if we play our football we can see what that means [for the title race].
"I don't have a proper explanation for tonight. To find one is my main concern, not how City are doing."
After conceding six at Manchester City on Boxing Day, Leicester's morale-boosting win moved them up to ninth in the standings.
"Given the context of the game on the back of Sunday [against City], the players put in a heroic performance given the recovery time and having played City," Rodgers said.
"The players were amazing how they coped. We had to defend for our lives. I am really pleased for the players tonight."
Liverpool, who had a five-day break prior to their trip to the King Power after Boxing Day's fixture against Leeds United was postponed, looked much fresher than Leicester, playing their second game in three days, and soon took control of the match.
After bombarding a Leicester backline decimated by injuries early on, Jordan Henderson volleyed Liverpool's first chance over, before Wilfred Ndidi fouled Salah in the penalty area to give the visitors a golden opportunity to break the deadlock.
The penalty from the Egyptian, however, was poor, too close to Schmeichel, with the rebound header from Salah coming out off the crossbar. It was the Liverpool striker's third penalty miss for the club in all competitions.
Since the start of 2020, Schmeichel has saved more penalties in the Premier League than any other goalkeeper, with Tuesday's stop his third in this period.
Salah then forced another fine save out of Schmeichel as Liverpool continued to throw everything at Leicester.
Mane's miss had the Liverpool bench looking at each other in disbelief, only for Lookman, following up his goal against champions Manchester City on Boxing Day, to add to their woes with a powerful finish after a swift counter.
There were last-ditch blocks aplenty, bodies put on the line, but Leicester got the job done, with the players sinking to their knees upon the final whistle, having left Liverpool unable to score for the first time in 29 league games.
"We needed some effort not to score tonight," Klopp added. "We had quite a few chances.
"I didn't like the intensity even in the beginning but sometimes we have starts like this and we lost rhythm and never found it back.
"Tonight I didn't like a lot in our game so we have to do better. We just weren't ourselves."