Bruno Fernandes' goal in the 55th minute was enough for Manchester United to win their second game in a row.
Man United held 56% of the ball with 6 shots that were on target.
Southampton put up a fight as well, holding 48% of the ball and attempting 5 efforts on goal, but David De Gea ensured that United emerged unscathed.
fresh signing In the second half, Casemiro made his debut and had flashes of brilliance.
In anticipation of the start of other games scheduled for Matchday 4, United has now climbed to sixth place.