The Reds' opponents put up significantly more of a fight than many might have anticipated, but in the end, Jurgen Klopp's men scored another goal inside second half stoppage time to pull themselves over the line.
After the victory, this is how the national media reacted to Liverpool making the final, which will take place on Saturday evening, with Flamengo the team standing in their way.
Andy Hunter of The Guardian praised the Reds' ability to step up to the big occasion despite illness and injury disrupting Klopp's men.
He wrote: "Different continent, different competition, same old Liverpool. The Club World Cup semi-final proved a complication for the European champions but Firmino found a familiar solution with a stoppage‑time winner against Monterrey.
"Teething troubles were inevitable, and Monterrey were alert to their opponents’ vulnerability in the air, but Liverpool’s control of possession – and Alisson’s assured performance – helped alleviate the pressure on their defence."
She wrote: "Salah was indisputably the main attraction on Wednesday night in the mammoth multi-purpose stadium. He contributed to the game’s first decisive moment, dividing Monterrey’s defence with a superb reverse pass behind Cesar Montes and Nicolas Sanchez, that Keita collected and converted with a first-time finish.
"Three minutes later, Liverpool failed to fully clear a free-kick and switched off on the second phase, with man-of-the-match Alisson making a save from Jesus Gallardo only for Rogelio Funes Mori to hit home the rebound.
"There was finally a moment to quicken the pulse and thankfully avert extra time on 91 minutes. Firmino, recently introduced into the action, produced a neat finish after Salah’s tenacity kept the play alive and Trent Alexander-Arnold threaded a clever ball through to him, sending Liverpool into Saturday’s final against Flamengo."
Chris Bascombe focused more on the changes that Klopp had made - and that it was a second game in as many days due to an unrelenting schedule across two continents.
Writing in The Telegraph , he said: "There was a moment in the Khalifa Stadium last night when Klopp probably wished he had gone to Villa Park instead.
"Liverpool were struggling, his line-up was unrecognisable from European champions, and the Monterrey coach, Antonio Mohamed – calling for Joe Gomez to be sent off – decided to mimic a gangster from Narcos, gesticulating to the Liverpool manager to compare the size of cojones.
"Klopp, increasingly frustrated by the combination of time-wasting, play-acting and all-around disruption from a Mexican side more competitive than imagined, was happy to accept the challenge."
The Reds showed plenty of fight as they ground out the win.
Bascombe concluded: "One of the most peculiar 24 hours in Liverpool history: two matches, 28 players, two cups and two continents. Kloppage time – so influential in the Premier League – evidently travels well."
The Mirror's Alex Richards' five talking points from the semi-final piece included the two goalscorers on the day, in Firmino and Keita.
He wrote: "When he was needed, he stepped up. Again. Much is made of Roberto Firmino's importance to this Liverpool side, and how he allows those alongside him to shine.
"But this was his moment, and one which fans, players and staff alike will all be delighted about. It was a classy finish from the Brazilian, to ensure a meeting with his compatriots on Saturday."
On Keita, he added: "There were glimpses of the Guinean's best in Qatar, as he showed what he can bring to this side with his ability to carry the ball through midfield and produce smart touches in and around the opposition final third.
"His overall display showed that he is seizing the opportunities handed to him after his recent comeback from injury."
The Reds will look to win their first ever Club World Cup title on Saturday night, before returning to Premier League action on Boxing Day with a trip to Leicester City.