Scott McTominay scored a screamer to send Man Utd into the lead on the stroke of half-time.
The sides had up to that point failed to create anything that really troubled the opposition bar a couple of tame efforts.
Andreas Pereira showed good footwork to sidestep David Luiz and shoot at goal but Bernd Leno got down well, before Nicolas Pepe forced a routine save out of David de Gea at the other end.
Marcus Rashford then blew a good chance for United as he took to long allowing Sokratis back to defend.
A good double save from de Gea looked to have brought the first half action to a close, but United got their noses in front.
Rashford made amends for his earlier lack of conviction, finding McTominay on the edge of the box who produced a strike of real quality to find the top corner and give his side the advantage.