The Brazil international scored in a 1-0 win against compatriots Flamengo in the extra period to ease the feeling of injustice which had unfolded deep into added time at the end of 90 minutes.
However, instead of a free-kick and red card for Rafinha Al Jassim awarded a drop-ball to Flamengo, just the latest on a night of strange decisions.
At that point it seemed it was going to be fourth time unlucky for Liverpool, who had come up short in this competition in 1981, 1984 and 2005.
You could almost hear a collective “told you so” from the critics back in England who felt Klopp should have prioritised the Carabao Cup – instead of sending out a youth team to get beat 5-0 by Aston Villa – over this tournament.
However, Firmino – who had missed the first chance after just 42 seconds – finished off a sweeping move started by Jordan Henderson, benefiting from Mane’s hold-up play and lay-off 10 minutes into the first 15 extra minutes.
It was an historic goal which saw the Reds become the first English side to win an unprecedented treble of Champions League, European Super Cup and Club World Cup.
FIFA’s plan was for this event to showcase Qatar’s footballing capabilities to the rest of the globe ahead of the 2022 World Cup controversially awarded to the Gulf state.
However, the appointment of a local official with a lack of experience for the final left organisers open to criticism.
The 32-year-old referee, who previous experience included the 2017 Under-17 World Cup and video assistant for the 2018 World Cup in Russia, was officiating the most high-profile game of his career.
But their early confidence and dominance soon waned as, with Flamengo happy to make the contest more of a scrap than a beauty contest, the Brazilians provided a test.
Firmino began the second half as he had done the first with an early chance, hitting the post with the ball spinning back across goal, with Salah stabbing an Alexander-Arnold cross wide.
Alisson Becker denied Gabriel Barbosa twice, once from an overhead kick, but everything seemed to be just that fraction off for Liverpool: passes fell short, first touches went long, and as a result they struggled to properly open up Flamengo.
That was amplified when Alex Oxlade-Chamberlain limped off having gone down thumping the turf in agony after a challenge saw his ankle buckle.
A well-offside Salah gave the mainly Arab crowd what they had come to see by putting the ball in the net but it was not until the 80th minute that Alexander-Arnold had the team’s first shot on target, quickly followed by Henderson forcing Diego Alves to tip over.
Then came the controversy and confusion with Rafinha remaining on a booking, initially benefiting from the law of double-jeopardy for conceding a penalty and then from the inaccurate application of the laws by the referee, who awarded a drop-ball and not a foul.
Thankfully Firmino found a way to decide the game without the need for official intervention and Salah and Van Dijk both had shots saved which could have put the result beyond doubt.
When substitute Lincoln blazed over in the final minute of extra time the job was done and Liverpool had completed their ‘moon landing’ in conquering the world.
They return home with a 66th trophy in the club’s history now focused on becoming champions of England, with the added bonus that Manchester City’s victory over Leicester ensured their lead at the top of the Premier League remains 10 points.