With just 6 minutes on the clock, a long ball forward towards Mohamed Salah saw Wesley Hoedt fluff his attempted clearance, allowing Salah to slide a perfectly-weighted ball across to the incoming Roberto Firmino on the edge of the home side's box.
It's tight in the Premier League and the teams can change around.
Indeed, Jurgen Klopp failed to sign a recognised striker in the summer but it has not been to the detriment of his side's progress this season.
Klopp's side could have added further gloss to the scoreline as they missed a couple more opportunities, but Southampton never looked like fighting back and Liverpool successfully capitalised on United's 1-0 defeat at Newcastle United earlier on Sunday.
LIVERPOOL, ENGLAND - JANUARY 27: Virgil van Dijk of Liverpool reacts during The Emirates FA Cup Fourth Round match between Liverpool and West Bromwich Albion at Anfield on January 27, 2018 in Liverpool, England.
He said: "Southampton's win at West Brom last weekend was big for them because they had waited so long for a Premier League win - 12 games and 10 weeks to be exact - and this game is a hard one to call". "
"Changing the game with counter attacks in Football playing moments, we would have liked to do a little better and the rythm was not too good either.".
The Reds have now lost just one of their last 18 Premier League games, whereas Southampton equal an unwanted club record of seven successive home games without a Premier League victory. "I think we deserved the three points, [we got a] clean sheet, no injuries - [it was] almost ideal".