Michail Antonio and Declan Rice struck in each half to secure a 2-0 win for West Ham against Dinamo Zagreb in Thursday's Europa League opener.
Antonio opened the scoring as he capitalised on Kevin Theophile-Catherine's poor pass to finish into an empty net, before Rice doubled the lead five minutes after the break.
Luka Ivanusec almost beat Lukasz Fabianksi, who did not make a save all game, but that was Dinamo's only opportunity as West Ham secured their first win in European competition since 1999 to top Group H.
In contrast, Dinamo will be disappointed with their efforts at the Maksimir Stadium as their 13-match undefeated run in the group stage of the competition ended abruptly.
The visitors boasted almost 70 per cent possession inside the opening 15 minutes but, barring a barrage of corners, Aaron Cresswell's inaccurate long-range effort was their only half-chance.
However, Antonio made West Ham's dominance pay as he profited from Theophile-Catherine's concentration lapse to round Dominik Livakovic and score the Hammers' first goal in Europe since 1999.
Ryan Fredericks was then denied by the Dinamo goalkeeper's feet before Nikola Vlasic fired narrowly wide on the stroke of half-time.
Dinamo looked to respond immediately in the second half, with Bruno Petkovic blasting narrowly wide but it was Rice who added a second, driving forward before powering a left-footed strike through the legs of Livakovic.
Ivanusec tried to pull one back, dancing around Kurt Zouma prior to curling towards the bottom-right corner, only to see his effort trickle wide as Fabianski passed the hour-mark without making a save.
With David Moyes' men dominant, Pablo Fornals looked for a third with a low attempt but found Livakovic's hands as the visitors cruised to a memorable return to European football.