The Reds began the season with a 4-1 victory over Norwich at Anfield, but defensive frailties were apparent in both that and the UEFA Super Cup triumph over Chelsea in midweek.
It was a difficult first half in Hampshire, but fortunately Sadio Mane kicked into gear in stoppage time, firing a brilliant curled effort beyond Angus Gunn to make it 1-0.
And Jurgen Klopp clearly had words in the dressing room, as Liverpool emerged for the second 45 a different beast, pushing relentlessly for a second.
Eventually, however, Firmino was able to fire past the ex-Man City youngster to give the Reds command of the tie, cutting inside and sending the ball low into the bottom corner.
That was not to be the last of the drama, though, as Adrian‘s shaky performance ultimately led to a shocking error from the Spaniard.
Fortunately it came too late, and Liverpool were able to hold on, with three points theirs as they return to Merseyside.
But with Arsenal to come next Saturday night, there were clear warning signs that need be to addressed.