Liverpool manager Jurgen Klopp is not concerned by his defensive options heading into the opening weekend of the season, despite being able to field only one senior centre back in the 3-1 friendly win over Torino.
Anfield gave Alisson a brilliant farewell, but the reception went up a level when Karius entered the fray.
With West Ham visiting Anfield for the Premier League opener on Sunday, Klopp withdrew most of his first string, giving run-outs to the likes of Daniel Sturridge, Adam Lallana, Danny Ings and Marko Grujic, along with another off-season recruit, Xherdan Shaqiri. His squad looks deep, sharp and impressive five days ahead of a league season carrying high expectation.
But while City begin the campaign as firm favourites after their record-breaking title campaign last season, they will be well aware of the threat posed by Juergen Klopp's improving Liverpool and the rest of the big six.
Within a matter of minutes Georginio Wijnaldum was in for Liverpool's second of the night.
Liverpool should have taken the lead moments earlier when gifted a hugely generous penalty by referee Michael Oliver. Wijnaldum and Salah combined to set up Firmino for a shot that deflected into the top corner off Lorenzo De Silvestri.
The performance seldom hit the emphatic heights of Saturday's 5-0 thrashing of Napoli and suffered something of a false start when new signing Fabinho swiped a penalty wide after Gleison Bremer tripped Sadio Mane.
Italy global Andrea Belotti pulled one back for the visitors with a powerful header, but after Klopp made a raft of substitutions, Daniel Sturridge nodded in a Xherdan Shaqiri cross to score for the third friendly in a row.
Jordan Henderson came on as a second-half substitute against Torino to make his first appearance of the summer, having been granted extra time off following the World Cup.