As mentioned, Van Dijk will play his first game for Liverpool against the side that he left just over a month ago for a world-record £75 million.
Southampton are third from bottom, a point behind 17th-placed Huddersfield Town who won earlier on Sunday.
The Reds dominated against the Saints this afternoon.
In the 14th minute, Reds goalkeeper Loris Karius did well to deny Pierre-Emile Hojbjerg's curling strike from just inside the box.
Who will come out on top in the battle of the managers Mauricio Pellegrino or Jürgen Klopp?
The two-goal lead was harsh on Southampton going into half time, but it nearly got worse in the opening stages of the second half when Mane's acrobatic effort was blocked and fell at the feet of Salah, although this time the prolific winger scooped his finish over the crossbar.
Firmino collected the ball from Salah before producing an exquisite flick back into the Egyptian's path, and Salah made no mistake with his finish into the bottom corner for his 29th goal of the season.
The Dutch defender completely missed his kick when trying to deal with a long ball and Salah pounced in a flash, showing great awareness to square to Firmino, who confidently slotted past Alex McCarthy.
In the 57th minute, Ward-Prowse delivered a unsafe cross which Wesley Hoedt failed to divert goal ward.
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