Record signing Marko Arnautovic scored his first West Ham goal in a 2-2 draw with Werder Bremen.
Austria forward Arnautovic, who signed from Stoke in a Â£20million deal which could rise by a further Â£5m, turned in Arthur Masuaku's deflected cross for a 25th-minute equaliser.
Luca Caldirola had given Bremen a 15th-minute lead in Lohne, with England goalkeeper Joe Hart unable to stop the close-range header on his Hammers debut.
Young Spanish striker Toni Martinez put West Ham ahead after 75 minutes when he headed home Andre Ayew's cross.
But Zhang Yuning, the China striker on loan from West Brom, struck nine minutes from time to hand Bremen the Betway Cup 3-2 on aggregate.
Bremen had won Friday's first leg in Schneverdingen 1-0.