Eintracht Frankfurt seized control of their Europa League semi-final against West Ham as Japan midfielder Daichi Kamada inspired a 2-1 win in the first leg on Thursday.
Oliver Glasner's side arrived at the London Stadium as underdogs against a West Ham team enjoying their best season for years.
But Ansgar Knauff gave Frankfurt the perfect start with a goal after just 49 seconds.
Michail Antonio equalised with his first goal in 11 matches, but Kamada bagged the winner with a close-range finish in the second half.
Frankfurt have struggled at times in the Bundesliga this season, saving their best performances for Europe.
They had already stunned Barcelona in the quarter-finals and this was another memorable performance, putting them in pole position to reach the final against RB Leipzig or Rangers.
Frankfurt, whose only major European title came in the 1980 UEFA Cup, can finish the job when they host the second leg on May 5.
"I'm very impressed by the lads, how they played, how they took the lead in the first minute," Glasner said.
"It's just impressive, the confidence they showed. West Ham threatened then, but we did well defending the set pieces.
"Leading after the first leg is always good, even though we were a little bit lucky from their bicycle kick."
Back in 1976, West Ham defeated Frankfurt 4-3 on aggregate in the European Cup Winners' Cup semi-finals.
Hoping to reach their first major European final since then, West Ham will have to stage an impressive escape act in Frankfurt to emulate that success.
"Not what we wanted. We didn't play well enough to get a result. We started slow in second half and gave away a poor goal for the second," West Ham boss David Moyes said.
"We missed an awful lot of opportunities to create chances. We had chances to cross the ball better and didn't take them. We missed big chances in the box.
