The question for Luiz Uehara and Darren Hart is how a team that plays so well in training can freeze on match day and not do itself justice.
''It's a mental thing,'' Uehara said.
''We must remember that these lads are quite young and inexperienced in football terms, and may feel under less pressure when they play away from home.
''So our task is to build confidence, as well as train for strategy and team shape. After only eight matches together, we have made progress, and will continue to do so.
''On Sunday, I will ask them to be brave and confident. They have been training very well, so we will see how their spirit is, on the day, and we need a strong, vigorous start.''
Reduced to spectator status, Henrique Viana is a forlorn figure in his plaster cast, covering a damaged metatarsal that is certain to eliminate the talented Brazilian from any further football this season.
The striker, who has scored four goals, will be missed but a ready replacement has stepped in. Regan Coldicott will play tomorrow and, hopefully, will bring with him the form that made him United's top scorer last year with seven goals.
Sturdy centreback Peter Overmire is still out with a cut foot, and both striker Peter Rae and defender Logan Wrightwebb will face late tests to check their fitness.
It is a revolving door at Southern United, and in come midfielders Aajay Cunningham and Morgan Day, back from a one-week suspension.
Centreback Matt Joy and keeper Tom Batty will play pivotal roles as Southern aims at a tighter defence and a midfield to match the Wellington visitor. In November's first-round away game, United was beaten 3-1 by Wellington. Viana gave Southern a shock early lead with a chest and volley that might yet qualify as the goal of the season.
A missed penalty might have narrowed the score further, but the classy Wellington side, which played with pace and tricky possession, laid siege to keeper Batty's goal for long periods.
Always a bagful of tricks, Wellington's Henry Fa'arodo and his jinking stop-start runs will need bottling, but fellow scorer Charlie Henry is injured, as is Tobias Bertsch.
However, entering the fray could be former Otago player Joel Stevens, who scored last week for Wellington.
Wellington coach Matt Calcott will want to at least consolidate third place in the ASB Premiership, behind Auckland and Canterbury.
''But we realise that Southern beat Waitakere by the same score as we did, yet also lost badly by six goals last week, so we are wary of a bounce-back situation.''
If Southern wins, it could leapfrog Waikato-BOP, which has played an extra match, but is only one point ahead.
At Tahuna Park, the Southern United youth team plays Manawatu at 1pm.
''Manawatu beat Canterbury 3-2, but lost 1-0 to Wellington,'' coach Mike McGarry said.
''We drew with Canterbury and are looking for a win from this game.''
Southern v Wellington: Forsyth Barr Stadium, tomorrow, 2pm
Southern United: Tom Batty, Nicholas Hindson, Matt Joy, Sam Mepham, Regan Coldicott, Aajay Cunningham Taylor McCormack, Peter Rae, Jefferson Potrich, Logan Wrightwebb, Morgan Day, Daniel Morris, Campbell Higgins, Jacob Schneider, Andrew Ridden, Campbell Attwood.
Wellington: Jacob Spoonley, Colin Murphy, Adam Cowan, Henry Fa'arodo, Cole Peverley, Cory Chettleburgh, Charlie Henry, Roy Kayara, Cameron Lindsay, James Musa, Sam Mason-Smith, Jamie De Abreu, Tom Doyle, Tobias Bertsch, Clayton Lewis, Justin Gulley, Hamish Watson, Joel Stevens, Andrew Blake, Daniel Clarke, Tamupiwa Dimairo.
