Southampton boss, Ronald Koeman said he was confident that Southampton can stay in the top four for the rest of the season.
Saints recorded a first win at Old Trafford since 1988, courtesy of a goal from substitute Dusan Tadic, to leapfrog United and go third in the Premier League following the 1-0 win.
They have not finished in the top four for 31 seasons, but Koeman feels their defensive resolve and character can enable them to stay in the Champions League places.
"If we keep the spirit and the organisation, we can keep in front in the table," he said in a news conference. "We have 11 clean sheets in 21 games. We defended well and the spirit was unbelievable."
Koeman was not shocked his side triumphed and praised them for not being intimidated by facing United's superstar players.
He added: "It was important in the end of December that we got a point against Chelsea and the three points against Arsenal [on New Year's Day]. That makes belief in the players. That is what you need if you are not a big club, belief in the players, who are not afraid of the name or the stadium. We learned that. I am not surprised we won today."