A youthful West Ham side beat FCSB 3-0 to become the first team to maintain a 100 per cent record in the group stages of the Europa Conference League.
Hammers boss David Moyes made 10 changes for the trip to Bucharest, handing debuts to teenagers Oliver Scarles, 16, and Divin Mubama, 18, from the start with top spot already assured.
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Pablo Fornals (40, 65) scored either side of Mubama's deflected header (56) - which was later awarded as a Joyskim Dawa own goal - as West Ham coasted to victory in Romania.
West Ham top Group B after winning all six of their games, with Anderlecht joining them in the knockout stages after sealing second place with a 2-0 win over 10-man Silkeborg, while FCSB finish bottom.
How the Hammers made history in Bucharest
West Ham had a nervy start in Bucharest against FCSB, who came into the game knowing they would finish bottom of the group regardless, with Ben Johnson and Vladimir Coufal making errors in possession at the back.
It was the debutants, Scarles and Mubama, that sparked West Ham into life as the latter nearly finished off a wicked low cross from his team-mate, only to be denied by FCSB goalkeeper Stefan Tarnovanu.
The breakthrough came from a looping long ball by Johnson to Fornals, which the Spaniard finished off with a sweet left-footed half-volley after some poor FCSB defending. Replays showed the goal would not have stood if VAR was in use.
Ten minutes after the break, Mubama thought he had doubled West Ham's lead with a debut goal, connecting with Coufal's cross from the right, only for UEFA to put it down as an own goal by FCSB defender Dawa.
Fornals struck again nine minutes later as he took advantage of Tarnovanu's spill from Scarles' cross by hammering in the rebound for his second of the night on his 150th West Ham appearance.
West Ham were comfortable enough for Moyes to bring on five more academy graduates - three of which were teenagers - as Freddie Potts, Keenan Forson, Harrison Ashby, Kamarai Simon-Swyer and Kaelan Casey played a part in their boyhood club's historic group-stage run.
'Great spirit at West Ham'
West Ham boss David Moyes to BT Sport:
"Hopefully we are getting future pressure on the boys in the first team. All the boys played really well. We could have scored more goals.
"I thought Oliver Scarles played exceptionally well. Divin [Mubama] got a goal, I know it is being classed as an own goal, but he is a young centre-forward and you could see how much it meant for him to score.
"They have a great spirit in the Under-23s. There is a great spirit at West Ham and everyone is pleased for these young players.
"Everybody wants an opportunity, you just hope they can grab it and I thought both of them did tonight."
Fornals: I'm happy for the young players
West Ham's Pablo Fornals told BT Sport:
"We were already qualified first in the group but that is the success of the team. We came here for a difficult game, they changed coach, everyone was ready for the game.
"We came with a lot of kids but this is another point to be really happy and grateful about because the academy is supporting the first team with very good players.
"I am happy for the players who had chance to play, they did really well."
Asked about his two goals on his return to the side: "We came here to do our best because this is our chance. Really happy for all the players today because it is important for us as well, not just individually but also for the rest of the players in the team because they know we are strong."
What's next?
West Ham will play three more games before the World Cup break. They host Crystal Palace on Sunday in the Premier League; kick-off 2pm. They then welcome Blackburn Rovers in the Carabao Cup on Wednesday November 9.
West Ham's final Premier League game is on Saturday November 12 when they host Leicester; kick-off 3pm.