[Goldmine]

The ball is round anything can happen... that's  when a team doesn't respect their opponents they lose games they r expected to win

True the ball is round. Anything is possible.  From record of H to H matches btw the two teams the last time that Southampton win against MU was in 2015/2016. Only once each yr by 1-0. Since then they either draw or lose to MU similarly by a 1 goal margin (3-2). Based on this record an upset cannot be ruled out. The Epl has just started and its too early to tell for sure who will win the match. 
From MU last season performances and their1st match win this season against LU by a big scoreline of 5-1, I think it will be tough for Saints to beat them. MU have many good players all round. They stand in good stead for the EPL title.