Jurgen Klopp's side went on to romp the Canaries 5-2, confirming their place in the next stage - but after a late Stuart Armstrong equaliser at Vicarage Road, they would be forced to wait for a replay to be played out before finding out who they'd be facing.
Held at St Mary's, the replay was much less of a tightly-fought contest, with Sekou Mara netting a brace before Che Adams slotted home as the Saints cruised to a 3-0 win.
Liverpool will be seeking as much silverware as possible following the announcement that Klopp would depart the club at the end of the season, and will therefore be eyeing up a ninth FA Cup.
Two games now stand between the Reds and an initial semi-final trip to Wembley, with the likes of Manchester United, Manchester City and National League South outfit Maidstone United all still in the competition.
However, the Saints will be dreaming of some cup magic - something this year's tournament hasn't lacked - as they look to cause a mammoth upset on their travels.
The fifth-round tie will be played at Anfield on Wednesday February 28, kicking off at 8pm GMT - with ITV broadcasting the match in the UK.