The Hammers had only been able to draw 2-2 with the Romanian side at Upton Park seven days previously and lived to regret their failure to make the most of that home advantage.
They were ahead in only the third minute when Manuel Lanzini capitalised on a poorly cleared corner but two quickfire goals from Constantin Budescu towards the end of the first half turned the tie on its head, the Astra man hitting a driven effort to restore parity before slotting home from the middle of the penalty area less than three minutes later.
It left West Ham needing a goal to force extra time but that crucial strike was not forthcoming for the London side, who are left to focus on their domestic campaign.
Despite heading to Romania on the back foot, Slaven Bilic – with one eye on Sunday's Premier League opener against Arsenal - picked a relatively inexperienced XI to keep alive his side's Europa League hopes, with Kyle Knoyle and Doneil Henry joining Lanzini in making their competitive bows for the club.
