Wanderers are determined to show struggling Portsmouth no mercy on Wednesday night.

Sam Allardyce has identified the source of relegation-threatened Pompey's problems to be their weak home form.

And the Reebok boss intends to add to opposite number Harry Redknapp's misery with a display of ruthless efficiency at Fratton Park.

With three Premiership defeats in a row behind them and five points adrift of the safety zone, Portsmouth are deep in trouble and desperate for a lift.

Allardyce does not intend to give it them when he sends out his Wanderers team with a game plan aimed at taking advantage of the South coast side's anxieties.

"We have to capitalise on the drain of confidence they must be feeling," the Wanderers boss said.

"If we keep the game nil-nil and tight, then the longer it goes on, the more anxiety will creep into their players and we have to make the most of it.

"Portsmouth's problem is that they have not achieved what they normally achieve on their own soil.

"This season they have been very passionate and very committed but they have lost too many games at home and that's why they are in the position they are in.

"When you are in that position, things seem to go against you and we have to capitalise on that."

Wanderers' form is in such contrast to their opponents that Allardyce admits he just cannot see his side being beaten at the moment.

Despite being without four African Nations Cup players and three long term injury victims, the 14 fit first teamers are continuing the march on three fronts.

"Beating Arsenal in the cup on Saturday keeps the ball rolling in all competitions," he said.

"When you produce the kind of performances and results we have been doing consistently, you grow in confidence.

"I've got nothing but praise for my players for what they have achieved while we have had people missing with injury and the African Nations Cup.

"But we must not let it peter out and die."

Allardyce will urge his players to match Portsmouth for effort to deny them room to play and then pick them off when the goalmouth chances come.

Allardyce believes Portsmouth's lack of form means the chances will come for Wanderers and that is where he will be looking to Kevin Davies to cause problems and in-form goalscorers Stelios and Jared Borgetti to pounce.

"We'll have to compete first and try to capitalise on what mistakes they might make or produce some quality," he said.

"Portsmouth won't give us any room to play the sort of football we've been playing recently so we'll have to battle it out first and earn the right to play.

"The first thing that is going to be asked of my players is a passionate, battling, determined performance against a Portsmouth side which will have its sleeves rolled up and full of blood and thunder.

"We'll have to match that.

"It might help us that they might be slightly more fatigued than us because they played their cup game on Sunday while we played on Saturday and we've got to use that to our advantage as well.

"But we have a team that is full of confidence and playing to the best of its ability and if we do that we will get a result."