Jim Smith believes Portsmouth can use tonight's game to reignite their season.
After an impressive start in the Premiership, Harry Redknapp's side have lost seven of their last nine games and now find themselves only two points above the drop zone.
However, assistant manager Smith believes a win at St Mary's would be just the tonic Portsmouth need to get them back on their feet.
"We are not playing as well as we were at the start of the season, but it only takes one thing to turn things around," Smith said.
"There is not as much pressure on us in this match as there would be in a Premiership game and we have told the players to go out and express themselves.
"The Premiership is the most important thing, but we owe it to the fans to put on a good show."
Redknapp has injury problems, with Shaka Hislop, Nigel Quashie, Vincent Pericard, Jason Roberts and Svetoslav Todorov all out injured.
Senegal midfielder Amdy Faye may be recalled after a month out with a knee injury and Mark Burchill is set to make his first appearance of the season on the bench.
Southampton striker Kevin Phillips is expected to recover from a virus, but left-back Graeme Le Saux is out with a hamstring injury.
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