Southampton travel to Merseyside in very good form, but Souness believes that Liverpool will take the three points from the contest.
"In our league nobody rolls over and you face a physical encounter from the first minute to the last," he said. "He'll see that on Sunday because Southampton have done quite remarkably under Ronald Koeman, especially when you consider the number of players that have left them in the last couple of years.
"However, I can only see Liverpool winning given the momentum that is with them."
Liverpool's momentum largely comes from their appointment of Jurgen Klopp, which has created plenty of optimism around the club again.
The Reds have actually made a slow start to the campaign, but Klopp's arrival at Anfield seems to have encouraged supporters that they can challenge for a European place.
Klopp has taken charge of two Liverpool games so far, but he is still waiting for his first win, having seen the side draw with Tottenham Hotspur and Rubin Kazan.
Southampton will be hoping to spoil the German manager's first Premier League game in the Anfield dug-out, and they should be full of confidence after their recent run of form.
The Saints have lost just once in their last seven matches across all competitions, making them one of the most in-form teams in England.