West Ham United fell to a first European defeat since May 2022 as Olympiacos claimed a 2-1 win at the Georgios Karaiskakis Stadium.
Kostas Fortounis opened the scoring for the Greek side in the first half when the Olympiacos captain stepped into midfield and fired a powerful effort home from 25 yards.
The host's advantage was doubled on the stroke of half-time when Rodinei whipped in a dangerous cross, which captian Angelo Ogbonna could only turn into his own net.
Lucas Paquetá's brilliant volley from outside the penalty box in the 87th minute halved the deficit, while Danny Ings and James Ward-Prowse also went close for the Hammers.
Despite the loss, West Ham remain top of Group A and have the opportunity to return to winning ways in Europe when Olympiacos visit London Stadium in two weeks.
Check out the highlights from Thursday's European fixture in the video player above.
