Olympiacos are leading Manchester United 1-0 after 45 minutes of their Champions League tie at the Karaiskakis Stadium.
Alejandro Dominguez threatened early on for the hosts after winning the ball in the midfield and driving into the box, before seeing his goalbound effort blocked by Nemanja Vidic.
The Greek side continued to create more of the chances, and Hernan Perez fired narrowly wide of the post with a strike from long range.
In the 38th minute of the match Olympiacos took the lead, as Giannis Maniatis fired in a low strike that was flicked on by Dominguez and diverted beyond the reach of David de Gea.
United almost responded immediately, as Kostas Manolas headed just over his own crossbar from Wayne Rooney's free kick.
