Liverpool were less affected by the demands of World Cup action than their title rivals and it has shown in their fine start to the season with four straight Premier League wins to sit top of the table.
Georginio Wijnaldum opened the scoring for Liverpool at Wembley before Firmino doubled the visitors' lead ten minutes after half-time.
Erik Lamela scored a late goal to set up a nervy finish but the Reds held on for three points.
Firmino was transported to Moorfields Eye Hospital to be assessed and manager Jurgen Klopp admitted after the game that he didn't know the severity of his forward's injury.
"They have the Champions League starting and the cup competitions to come so we'll see how they get on, but it's a strong start". "We could have scored more and we controlled the game".
"I have no clue what exactly happened", said Klopp.
"We ask too much from the players, we constantly want them ready and if they are not we are not happy".
Liverpool's performances early in the 2018-19 season are reminiscent of Barcelona at their very best, according to club legend Graeme Souness.
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The Reds made it five consecutive wins as they continue their impressive start to the Premier League.
"I don't wait for problems, but I am old enough to know they will come".
But despite the win, the victory was soured by what was a horrific injury suffered by Firmino.
The Brazilian was forced off in the 74th minute following a battle with Jan Vertonghen and then sent for further examination.
"But it's something with the eye and for sure at the moment it's not comfortable for him".
Thankfully, Firmino had some good news for fans after being released from hospital with the diagnosis being an abrasion of the left eye.
I had to look at the incident three times, then finally in slow motion to see if there had been contact.
"Firmino travelled back to Merseyside separately from his teammates with club doctor Andy Massey following the positive assessment".