West Ham’s record-breaking 17-game unbeaten European run was ended by Olympiakos after a 2-1 Europa League defeat in Greece.
The Hammers, who had become the first English side to go 17 consecutive European matches unbeaten, conceded two first-half goals to halt their perfect start to this season's Europa League.
Olympiakos captain Kostas Fortounis opened the scoring in the 33rd minute with a powerful toe-poked strike from the edge of the box.
The home side then doubled their lead in first-half stoppage-time when West Ham skipper Angelo Ogbonna sliced into his own net.
West Ham, who made seven changes for the game in Pireaus, were given hope of a late comeback thanks to a fine first-time volley from substitute Lucas Paqueta in the 87th minute, but Olympiakos held on for victory despite eight minutes of added time.
With that, West Ham’s unbeaten record in Europe was at an end. It brought back bad memories for Moyes, who lost here with Manchester United in February 2014, a defeat described as the beginning of the end for him at Old Trafford.
West Ham remain top of Group A, although they are now level on points with German side Freiburg after their 3-1 win at bottom side TSC, while third-place Olympiakos are now just two points behind the Hammers.
The only bonus is Hammers will not have to wait long to exact revenge on Olympiacos in the reverse fixture on November 9.
What's next?
West Ham return to Premier League action on Sunday when they host Everton, live on Sky Sports - kick-off 1pm.
The Hammers then welcome Arsenal to the London Stadium for a Carabao Cup clash on Wednesday, live on Sky Sports - kick-off 7.30pm.
Olympiakos' next game is away to OFI in the Greek Super League on Monday - kick-off 2pm.