Saints boss Ronald Koeman knows that a perfect performance is needed if Saints are to turn over Manchester United on their own patch for a second year.
Speaking ahead of the clash at Old Trafford Koeman said.
"It's to try to play the same way, with the same attitude, the same confidence, and we showed it away against West Ham,” he told youtube.com/southamptonfc.
"I think maybe that was the best 45 minutes of this season and we know we have to play that level."
"We can't make stupid mistakes, because they are quality players, a quality team, they will punish you for those kind of mistakes and we need a perfect game to win on Saturday.”
"Our ambition is to win every game and to show good football, and we think if we play out of our qualities then we have a chance against everybody.
"I think they show what you can expect. Maybe they have a little bit difficulties to score goals, but they don't concede a lot and it's difficult to beat them, and for them it's difficult to win the game.
"They had a fantastic result against Liverpool last week and that gives everybody at Man U a boost and they like to continue, but still they fight for a high position on the table, in my opinion a position where the team needs to be. It's a tough one, but we know we can beat them.”