A depleted Glentoran side lost 2-0 to Ukranian side Vorksla Poltava in their Europa League second qualifying round first leg tie at the Oval.
Roman Bezus headed home from six yards in the 29th minute after a corner was deflected in his direction.
The Glens' best chance of the game fell to Ciaran Martyn but his header was cleared off the line.
Ahmed Januzi powered through the defence and fired a shot past Aaron Hogg for the second on 38 minutes.
The sides meet again in Ukraine next Thursday with Glentoran facing a major uphill struggle.