Romelu Lukaku equalled a Manchester United Premier League record with the only goal in a 1-0 win at Southampton.
The striker's close-range finish on 20 minutes means no player has scored more goals in their first six appearances for the club than Lukaku's six, level with Louis Saha.
Man Utd nearly had a second before the break but Marcus Rashford's 25-yard free-kick flew narrowly wide of Fraser Forster's post.
Southampton could not find an equaliser despite an improved second half, with Oriol Romeu's dragged effort the closest Mauricio Pellegrino's side came.
United are still unbeaten but are behind leaders Manchester City on goal difference. Saints drop to 11th.
See: Southampton report | Man Utd report